A  YEAR  IN  SCIENCE 


A  TEXT-BOOK  FOR  FIRST  YEAR  IN 
HIGH  SCHOOLS 


ADA  L.  WECKEL,  M.S. 

.  HEAD   OF   BIOLOGY    DEPARTMENT,    OAK   PARK    AND    RIVER 

FOREST   TOWNSHIP    HIGH    SCHOOL,   OAK 

PARK,    ILLINOIS 

AND 

JOSEPH  L.  THALMAN,  A.M. 

FORMER    HEAD   OF   BIOLOGY    DEPARTMENT,    OAK    PARK    AND   RIVER 

FOREST   TOWNSHIP    HIGH    SCHOOL  ;    PRINCIPAL    OF 

HIGH    SCHOOL,    NEW   CASTLE,    PA. 


CHICAGO  NEW    YORK 

ROW,  PETERSON  AND  COMPANY 


COPYRIGHT,  1916 
ROW,  PETERSON 
AND  COMPANY 


PREFACE 

The  history  of  the  many  attempts  to  fit  the  different 
special  sciences  into  the  first  year  of  the  high  school  is 
too  well  known  to  require  comment.  As  a  result  of  these 
experiences,  the  conviction  is  becoming  general  that  no 
one  science  is  adequate  for  an  introductory  course.  In 
the  last  few  years  the  effort  to  present  to  the  pupil  subject 
matter  of  interest  to  him,  adapted  to  his  stage  of  mental 
development,  and  at  the  same  time  of  educative  value,  has 
resulted  in  the  development  of  many  courses  in  general 
science.  These  courses  vary  somewhat  in  the  organiza- 
tion of  subject  matter  and  in  the  method  of  presentation, 
but  all  of  them  are  based  upon  the  conviction  that  the 
first  year  of  science  should  be  fundamental  to  all  the 
sciences. 

In  presenting  this  course  we  feel  that  it  meets  these 
fundamental  requirements,  first,  in  providing,  a  ground 
work  in  physics,  chemistry,  botany,  zoology,  physiology, 
and  physical  geography;  and  second,  that  it  has  stood 
the  test  of  time.  It  has  been  carried  through  about  fif- 
teen years  of  experimentation  in  which  frequent  changes 
in  material  as  well  as  eliminations  and  additions  have 
been  made,  until  it  has  now  become  fairly  well 
established. 

The  course  has  for  its  purpose  not  so  much  the  devel- 
opment of  the  subject  alone  as  the  consideration  of  that 
most  important  factor  in  teaching,  namely,  the  develop- 

v 

359396 


vi  PREFACE 

raent  of  the  pupil.  We  hope  that  the  scientific  informa- 
tion will  enable  him  to  appreciate  better  the  natural  phe- 
nomena going  on  around  him.  The  scientific  training 
should  enable  him  to  observe  more  accurately,  to  inter- 
pret more  sanely,  to  understand  the  vital  importance  of 
every  day  affairs,  and,  perhaps  most  important,  to  train 
him  to  apply  acquired  knowledge  to  useful  ends  and 
thus  become  a  better  citizen  of  his  community. 

We  wish  to  express  our  sincere  appreciation  to  Mr. 
J.  C.  Hanna,  High  School  Supervisor  for  the  State  of 
Illinois,  formerly  principal  of  the  Oak  Park,  Illinois, 
High  School,  for  writing  the  Introduction  and  for  his 
untiring  inspiration  and  advice  during  the  seven  years 
in  which  we  have  been  developing  this  course.  It  is  due 
to  Mr.  Hanna 's  firm  belief  in  the  general  science  idea 
that  this  work  has  become  a  reality. 

We  wish  also  to  express  our  appreciation  for  the  advice 
and  criticisms  given  us  by  the  teachers  who  have  been 
associated  with  us  in  the  teaching  of  this  course,  espe- 
cially for  the  valuable  suggestions  and  assistance  in  proof 
reading  by  Miss  Rachel  Ott  and  Miss  Ruth  Williston 
of  the  Oak  Park  High  School,  and  by  Mr.  F.  L.  Orth, 
Head  of  the  Science  Department  of  the  New  Castle,  Pa., 
High  School. 

To  all  who  have  in  any  way  contributed  in  the 
preparation  of  this  work,  we  hereby  make  grateful 
acknowledgment. 

A.  L.  W. 
J.  L.  T. 


INTRODUCTION 

Many  sincere  and  intelligent  persons  have  criticized  the 
public  school  as  an  institution  that  clings  too  closely  to 
obsolete  aims  and  outworn  methods. 

Some  text  books,  instead  of  ignoring  this  criticism  or 
indignantly  resenting  it,  have  attempted  to  meet  it  and 
to  correct  such  tendencies  as  are  really  faults. 

This  publication  by  Mr.  Thalman  and  Miss  Weckel 
seems  to  the  writer  to  be  one  of  the  most  earnest  and 
carefully  prepared  of  the  books  made  with  that  aim.  This 
fact,  as  being  distinctly  related  to  the  most  far-reaching 
administrative  problems,  may  justify  the  preparation  of 
this  introduction  by  one  who  is  not  a  scientist. 

Among  the  faults  that  have  been  observed  in  high- 
school  science  teaching,  two  have  seemed  conspicuous  and 
at  the  same  time  possible  to  remedy.  The  writer  is  there- 
fore glad  to  commend  what  appears  to  him  to  be  a 
thoroughgoing  and  workable  plan  for  eliminating  those 
faults. 

First,  the  material  presented  to  beginners  was  too  diffi- 
cult for  them  and  was  not  well  adapted  to  their  need 
and  their  stage  of  development.  Second,  the  attention 
of  the  beginners  was  for  a  year  confined  to  the  narrow 
limits  of  one  or  another  of  the  fields  into  which  scientific 
phenomena  are  for  many  purposes  very  properly 
grouped. 

vii 


viii  INTRODUCTION 

These  faults  have  tended  to  make  first  year  science 
courses  inadequate,  unfair,  and  likely  to  dull  the  edge 
of  interest. 

Surely  the  youth  on  the  borderland  of  the  New  World, 
standing  on  the  pinnacle  of  his  fresh  enthusiasm,  has  the 
right  to  a  "look  over"  of  the  field,  a  general  survey, 
before  he  takes  up  chain  and  transit  for  a  detailed  sur- 
vey, has  a  right  to  a  "bird's  eye  view"  before  he  begins 
confining  his  attention  to  a  "toad's  eye  view"  in  some 
particular  section  of  the  garden  of  nature. 

The  course  here  presented  is  the  outcome  of  the  desire 
suggested  above,  and  of  continued  experimentation 
extending  over  more  than  fifteen  years,  to  realize  a  course 
for  first  year  pupils  that  should  fill  the  following 
conditions : 

1.  A  course  that  should  introduce  the  pupil  to  the 
observing  of  natural  phenomena  and  the  recognizing  of 
natural  laws  in  a  manner  adapted  to  the  stage  of  his 
maturity,  and  likely  to  hold  and  maintain  his  interest 
and  stimulate  his  growth. 

2.  A  course  that  should  serve  the  purpose  of  training 
him,  not  only  to  observe  with  accuracy,  but  to  think  to 
just  conclusion  from  the  data  thus  gathered. 

3.  A  course  that  should  furnish  him,  in  this  process, 
with  information  which  he  is  likely  to  find  useful  in  his 
daily  life  and  which  he  may  thus  have  stored  in  his 
memory,  or  which  he  may  thus  be  trained,  as  he  needs 
it,  to  go  and  get,  with  pleasure  and  ease  and  success, 
by  further  study  or  by  consulting  references. 


INTRODUCTION  IX 

4.  A  course  that  should  prepare  the  way  for  any 
further  systematic  science  study  that  may  attract  him 
or  be  needful. 

5.  A  course  that  should  conform  to  the  Illinois  state 
law  which  requires  that  all  pupils  below  the  second  year 
of  the  high  school  and  above  the  third  year  of  school 
work  shall  study  physiology  and  hygiene  (including  the 
nature  of  alcoholic  drinks  and  other  narcotics)  for  not 
less  than  four  lessons  a  week  for  ten  or  more  weeks  of 
each  year. 

Though  several  text  books  in  General  Science  have  pre- 
ceded the  present  one  in  date  of  publication,  the  present 
course  was  in  successful  operation  for  several  years 
before  any  of  them  appeared. 

The  original  idea  was  that  of  the  present  writer,  but 
the  credit  for  the  work  done  belongs,  of  course,  to  the 
zeal,  loyalty,  patience,  and  skill  of  the  several  specialists 
who,  from  1899  to  the  present  time  set  themselves  to  the 
solution  of  the  problem  set  forth  above.  While  several 
instructors  did  much  in  the  earlier  years  to  clear  the 
ground,  the  book  itself,  as  it  stands,  is  the  work  of  the 
authors  named  on  the  title  page.  They  are  abundantly 
entitled  to  the  credit  that  will  be  given  them  for  making 
real  a  vague  idea  which  was  in  the  mind  of  another  when 
they  were  little  children. 

The  test  of  actual  class-room  experience  with  from  ten 
to  nineteen  classes  a  year  has  only  confirmed  all  con- 
cerned in  these  beliefs: 

1.     That  certain  preliminary  science  study  of  some 


x  INTRODUCTION 

sort  should  be  done  in  the  high  school  before  the  regu- 
larly accepted  laboratory  courses  in  physics,  chemistry, 
botany,  zoology,  and  physiography  are  taken  up ; 

2.  That  such  elementary  studies  are  advisable  for  all 
pupils,  whether  the  more  advanced  laboratory  work  is 
taken  up  later  or  not; 

3.  That,  aside  from  the  training  value  in  such  studies, 
consideration  should  be  given  to  the  matter  of  content 
with  reference  to  the  practical  usefulness  of  the  actual 
knowledge  acquired ;  such  consideration  will  demand  the 
study  of  elementary  truths  that  might  be  classified  under 
several  different  heads,  as  physics,  chemistry,  physiology, 
botany ; 

4.  That  useful  familiarity  may  thus  be  acquired  with 
simple  laboratory  methods  and  apparatus  which  will  save 
time  in  the  pursuance  of  more  advanced  courses; 

5.  That  some  familiarity  with  the  scientific  method  of 
attack  thus  acquired  in  dealing  with  experiments  under 
several  heads,  as  physics,  physiology,  botany,  etc.,  will 
tend  to  develop  early  the  "scientific"  habit  which  will  be 
of  use  in  every  department  of  study; 

6.  That  this,  and  the  other  aims  enumerated,  may  be 
reached  better  by  such  a  course  than  by  any  course  con- 
fined to  the  facts  and  problems  of  any  one  of  the  fields 
of  study  named  above. 

It  has  been  said,  in  the  preface  to  a  late  text  in  high- 
school  physics,  that  the  presentation  of  that  subject  in 
the  secondary  school  "  should  be  the  expansion  of  the 
every-day  life  of  the  pupil  into  the  broader  experience  or 


INTRODUCTION  XI 

observation  of  those  whose  lives  have  been  devoted  to 
the  study. " 

This  might  be  set  forth  as  the  guiding  principle  for  the 
study,  not  merely  of  "physics",  but  for  the  study  of 
the  material  phenomena  of  nature,  of  that  which  we  call 
Science. 

General  Science  in  some  form,  as  the  introductory  unit, 
has  come  to  stay.  It  will  last  longer  than  will  its  timid 
opponents.  The  somewhat  noisy  war  over  the  "project 
plan"  will  subside. 

A  thoughtful  examination  of  the  course  as  presented  in 
this  book  and  the  laboratory  manual  which  accompanies 
it,  and  above  all  experiment  with  it,  will  show  whether 
it  is  a  working  out  of  that  plan  of  framing  a  course, 
but  what  is  of  far  greater  importance,  such  trial  of  it 
will  show  whether  it  supplies  a  real  need  in  the  first 
high  school  year,  and  whether  it  helps  to  drown  the  many 
voiced  criticism  of  secondary  school  instruction  as  being 
unrelated  to  "real  life." 

JOHN  CALVIN  HANNA. 
Illinois  State  Supervisor  of  High  Schools, 
Springfield,  Illinois. 


CONTENTS 

PAGE 

CHAPTER  I.    MATTER 1 

What  we  understand  by  Science;  Definition  of  matter; 
Is  air  matter;  Three  forms  of  matter. 

CHAPTER  II.    CONSTITUTION  OF  MATTER 6 

Introduction:  Some  common  observations;  Molecular 
theory;  Molecules  in  solids;  Molecules  in  liquids;  Molecules 
in  gases;  Molecules  in  different  states;  Different  sizes  of 
molecules  and  inter-molecular  spaces. 

CHAPTER  III.    EFFECT  OF  HEAT  ox  MATTER 13 

Effect  Of  heat  on  solids;  Effect  of  heat  on  liquids;  An 
exception  to  the  rule;  The  effect  of  a  change  of  tempera- 
ture upon  gases. 

CHAPTER  IV.    TRANSFER  OF  HEAT 20 

Conduction;  Tireless  cookers;  Explanation  of  conduction; 
Convection;  Convection  due  to  displacement  of  molecules. 

CHAPTER  V.  MEASUREMENT  OF  TEMPERATURE;  THERMOMETRY.  26 
Introduction;  Galileo's  thermometer;  Mercury  thermome- 
ters; Fahrenheit;  Centigrade;  Construction  of  centigrade 
thermometer ;  Determination  of  freezing  and  boiling  points ; 
Value  of  a  centigrade  degree  in  terms  of  Fahrenheit  and 
vice-versa:  Range  of  mercury  thermometer;  Unit  of  heat 
measure. 

CHAPTER  VI.    CHANGES  IN  STATE  OF  MATTER 34 

Three  states  of  matter;  Change  from  solid  to  liquid,  and 
liquid  to  gas;  Quantity  of  heat  necessary  to  change  ice  to 
water;  Heat  necessary  to  dissolve  a  substance;  Heat  given 
off  when  liquids  become  solids;  Melting  points;  Boiling 
points;  Distillation;  Effect  of  change  of  pressure  on  boil- 
ing point;  Quantity  of  heat  used  in  changing  water  to 
steam;  Heat  withdrawn  in  evaporation  of  liquids;  Arti- 
ficial ice ;  Heat  given  off  in  condensation ;  Change  in  volume 
resulting  from  change  in  state;  Molecular  changes  resulting 
from  change  in  state. 

xiii 


CONTENTS 


PAGE 
CHAPTER  VII.    PHYSICAL  AND  CHEMICAL  CHANGES  ..........     51 

Physical  change;  Chemical  change. 

CHAPTER  VIII.     CHEMICAL  PHENOMENA  ...................     53 

Physical  and  chemical  properties;  Classification  of  matter; 
Mechanical  mixtures;  Chemical  compounds;  Elements; 
Number  of  elements  ;  Chemical  synthesis  ;  Chemical  analy-  ; 
sis;  Chemical  affinity. 

CHAPTER  IX.    CARBON  ....................................     60 

Introduction;  Charcoal;  Uses  of  charcoal;  Lampblack; 
Coal  ;  Graphite  ;  Diamond  ;  Carbon  dioxide  —  C02  ;  Prepara- 
tion and  test  for  carbon  dioxide;  Balance  of  carbon  dioxide 
maintained;  Commercial  uses  of  carbon  dioxide. 

CHAPTER  X.    PHOSPHORUS  ................................     72 

Introduction;  Preparation;  Properties;  Uses  of  phos- 
phorus; Friction  match;  Safety  match;  Dangers  of  friction 
match. 

CHAPTER  XI.    SULPHUR  ....  .............  .................     77 

Occurrence;  Preparation;  Physical  properties;  Chemical 
properties;  Uses. 

CHAPTER  XII.    IRON  .....................................     84 

Introduction;  Occurrence;  Preparation  from  ore;  Three 
forms  of  iron. 

CHAPTER  XIII.     OXYGEN  .................................     00 

4"-*~  Introduction;    Preparation;    Properties;    Oxidation;    Uses; 
Source. 

CHAPTER  XIV.     HYDROGEN  ...................  ............     97 

L  —  Occurrence;  Preparation;  Properties;  Uses. 

CHAPTER  XV.    NITROGEN  .....................  ............   101 

Occurrence;    Preparation;   Properties;   Uses. 
CHAPTER  XVI.    ACIDS,  BASES,  AND  NEUTRAL  SUBSTANCES  .  .  .   105 

Introduction;     Acids;     Characteristics    of    acids;     Bases; 

Characteristics  of  bases;  Neutralization;  Salts. 
CHAPTER  XVII.    WATER  ..................................   110 

Introduction;  Composition;  Properties  and  uses;  Hard  and 

soft  water;  Plant  and  animal  life  dependent  upon  water; 

Dangers  in  water. 


CONTENTS  xy 

PAGE 

CHAPTEB  XVIII.    ATMOSPHERE... 120 

Introduction;  Composition;  Properties  and  uses;  Moisture 
in  atmosphere ;  Dew  point ;  Dew  and  frost ;  Fog  and  clouds ; 
Rain;  Snow  and  hail. 

CHAPTER  XIX.    ATMOSPHERIC  PRESSURE 129 

Introduction;  Air  presses  in  all  directions;  Column  of 
mercury  held  by  air  pressure;  Variations  in  pressure  due 
to  elevation ;  Barometer ;  Uses  of  the  barometer. 

CHAPTER  XX.    WINDS  AND  STORMS 137 

Winds;  Cause  of  winds;  General  effect  of  unequal  heating; 
Land  and  sea  breezes;  Cyclones;  Thunderstorms;  Torna- 
does; Effect  of  winds  on  rainfall. 

CHAPTER  XXI.    WEATHER  AND  CLIMATE 149 

Weather;  Climate;  Effect  of  temperature  on  climate;  Day 
and  night;  Seasons;  Weather  maps;  Explanation  of  a 
weather  map. 

CHAPTER  XXII.    THE  SURFACE  OF  THE  EARTH 160 

Continents  and  oceans;  Mountains,  plateaus,  and  plains; 
Minor  land  forms;  Effect  of  the  atmosphere  on  the  earth's 
surface;  Effect  of  change  of  temperature  on  rocks;  Chemi- 
cal; Work  of  rain  in  causing  relief. 

CHAPTER  XXIII.    STREAMS  AND  THEIR  WORK 172 

Introduction;  Streams  and  stream  erosion;  Stream  develop- 
ment; Maturity;  Old  Age;  Accidents  to  stream  develop- 
ment; Streams  as  factors  in  human  activities. 

CHAPTER  XXIV.    SOIL 186 

Introduction;  Origin;  Kinds;  Clay;  Sand. 

CHAPTER  XXV.    INTRODUCTION  TO  PLANTS 193 

Importance  of  plants;  Plants  are  composed  of  cells;  Com- 
position of  protoplasm;  Properties  of  protoplasm;  Com- 
parison of  plants  and  animals. 

CHAPTER  XXVI.     LEAVES 200 

Structure  of  leaves;  Chlorophyll;  Food  making;  Food  stor- 
age; Other  foods  manufactured  by  plants;  Uses  of  food; 
Transpiration ;  Disadvantages  of  transpiration ;  Advantages 
to  plant;  Habitat  dependent  on  water  supply;  Protection 
against  loss  of  water;  Respiration;  Air  storage. 


xvi  CONTENTS 

PAGE 

CHAPTER  XXVII.     ROOTS 219 

Function;  Structure;  Absorption  of  water  and  solutes; 
Anchorage. 

CHAPTER  XXVIII.     STEMS 225 

Functions;  Kinds;  Structure. 

CHAPTER  XXIX.     REPRODUCTION 232 

Reproduction  and  nutrition;  Flowers;  Formation  of  seeds; 
Pollination;  Seed  dispersal. 

CHAPTER  XXX.    IMPORTANCE  OF  PLANTS  TO  MAN 242 

Economic  importance;  Bacteria;  Conditions  for  growth 
of  bacteria;  Bacteria  and  disease;  Decay;  Useful  bacteria. 

CHAPTER  XXXI.    ANIMALS 240 

Distribution;  Means  of  distribution;  Factors  determining 
distribution;-  Barriers  to  distribution;  Animals  can  not 
maintain  their  ground;  Change  due  to  new  conditions; 
Adaptation. 

CHAPTER  XXXII.    GROUPS  OF  ANIMALS 254 

General  statement;  Mammals;  Birds;  Reptiles;  Amphi- 
bians; Fishes;  Arthropods;  Mollusks;  Worms;  Echino- 
derms;  Coelenterates ;  Porifera;  Protozoa. 

CHAPTER  XXXIII.    LIFE  PROCESSES  IN  ANIMALS 272 

Ameba;  Complex  animals;  Tissues,  organs,  and  systems; 
Animal  functions;  Digestion;  Respiration;  Circulation; 
Excretion;  Motion;  Sensitiveness;  Reproduction. 

CHAPTER  XXXIV.    RELATION  OF  ANIMALS  TO  MAN 286 

General  statement;  Animals  useful  to  man;  Domesticated 
animals;  Food-supplying  animals;  Animals  supplying 
clothing;  Animals  injurious  to  man;  Diseases  produced 
and  carried  by  animals;  Animals  injurious  to  crops. 

CHAPTER  XXXV.    MAN'S  PLACE  IN  NATURE 294 

Classification;  Differences  between  man  and  other  primates; 
Age  and  races  of  man;  The  human  body. 

CHAPTER  XXXVI.    FOODS 298 

Introduction;  Elements  in  food;  Use  of  food;  Foodstuffs; 
Proteins;  Test  of  protein;  Carbohydrates;  Starch;  Test 
for  starch;  Sugar;  Test  for  sugar;  Fats  and  oils;  Test 
for  fats  and  oils;  Mineral  salts  or  inorganic  foods;  Water. 


CONTENTS 


XVll 


PAGE 

CHAPTEB  XXXVII.    COMPOSITION  OF  FOODS 304 

Content  of  foods;  Use  of  foodstuffs;  Building  material; 
Fuel;  Quantity  and  kind  of  food;  Selection  of  food; 
Adulteration ;  Cooking. 

CHAPTER  XXXVIII.    DIGESTIVE  SYSTEM 310 

Introduction;  Alimentary  canal;.  Digestive  glands;  The 
mouth;  Teeth;  Structure  of  tooth;  Care  of  the  teeth;  The 
tongue;  Salivary  glands;  Throat  or  pharynx;  Esophagus; 
Stomach;  Intestines;  Liver;  Pancreas;  Peritoneum  and 
mesentery. 

CHAPTER  XXXIX.     DIGESTION 321 

Introduction ;  Necessity  of  digestion ;  Action  upon  food ; 
Digestion  in  mouth;  Digestion  in  stomach;  Digestion  in 
intestine;  Large  intestine;  Absorption. 

CHAPTER  XL.    NARCOTICS  AND  STIMULANTS 328 

Characteristics;  Stimulants;  Tobacco;  Opium  and  other 
narcotics;  Alcohol;  Conclusion. 

CHAPTER  XLI.     CIRCULATORY  SYSTEM 334 

Introduction;  Blood;  Lymph;  Red  corpuscles;  White  cor- 
puscles; Coagulation;  Amount  of  blood;  The  heart  struc- 
ture; Action  of  heart;  Beat;  Blood  and  lymph  vessels; 
Lymph  vessels. 

CHAPTER  XLII.    RESPIRATORY  SYSTEM 345 

Need  of  air;  Oxidation;  Internal  and  external  respiration; 
Organs  of  respiration;  Nose  cavity;  Larynx;  The  lungs; 
The  pleura;  Mechanism  of  breathing;  Comparison  of  in- 
haled and  exhaled  air;  Necessity  of  ventilation;  Methods 
of  ventilation;  Diseases  of  the  respiratory  organs;  Ade- 
noids; Tonsils;  Pleurisy;  Contagious  diseases. 

CHAPTER  XLIII.     EXCRETORY  SYSTEM 357 

General ;  The  kidneys ;  The  skin ;  Structure ;  Sweat  glands ; 
The  hair;  The  nails;  Temperature  of  the  body;  Source 
of  heat;  Cooling  the  body;  Clothing;  Care  of  the  skin. 

CHAPTER  XLIV.     DUCTLESS  GLANDS 367 

Introduction;  Lymph  glands;  Adrenal  bodies;  Thyroid 
glands;  The  spleen;  The  pancreas. 


CONTENTS 


PAGE 

CHAPTER  XLV.    SKELETAL  SYSTEM  ........................  370 

General;  Kegions  of  the  skeleton;  The  head;  The  trunk; 
Ribs  and  sternum;  Bones  of  limbs;  Composition  of  bone; 
Growth  of  bone;  Joints;  Hygiene  of  the  skeleton. 

CHAPTER  XLVI.     MUSCULAR  SYSTEM  ......................   378 

Importance;  Structure;  Blood  and  nerve  supply;  Action  of 
muscles;  Results  of  muscular  action;  Exercise. 

CHAPTER  XLVII.    NERVOUS  SYSTEM  .......................   383 

Introduction;  Parts  of  nervous  system;  The  nerve  cell; 
Nerves;  The  brain;  Functions  of  brain;  Spinal  cord;  Sym- 
pathetic nervous  system;  Action  of  nervous  system;  Reflex 
actions;  Voluntary  action;  Habits;  Education;  Care  of 
nervous  system. 

CHAPTER  XLVIII.    THE  SPECIAL  SENSES  ...................  397 

General;  Touch;  Temperature;  Taste;  Smell;  Eye;  Struc- 
ture; Light;  Lenses;  Images;  Focusing;  Defects  of  the 
eye;  Care  of  the  eyes;  The  ear;  Structure  of  the  ear; 
Action  of  ear;  Care  of  ears. 

CHAPTER  XLIX.     HEALTH  AND  DISEASE  ...................  411 

Importance  of  health;  Health  and  disease;  Cause  of  dis- 
ease; How  germs  enter  the  body;  Growth  of  germs;  How 
the  body  destroys  germs;  Treatment  of  disease;  Serums; 
Vaccines;  Medicines;  Immunity. 

CHAPTER  L.    SANITATION  .................................  421 

Importance;  Preventable  diseases;  Destruction  of  germs; 
Disinfection;  Fumigation;  Quarantine;  Food;  Insects  and 
disease;  Milk;  Water;  The  Board  of  Health. 


A  YEAR  IN  SCIENCE 

CHAPTER  I 
MATTER 

What  we  understand  by  Science.  The  subject  with 
which  we  are  about  to  deal  in  this  study  is  Science. 
To  many  this  is  a  new  study,  and,  no  doubt,  ideas  of  its 
meaning  differ  widely.  However,  we  shall  learn,  as  we 
proceed  with  this  work,  that  we  are  dealing  with  very 
common  things  and  common  changes  that  are  going  on 
about  us  daily. 

Some  of  the  subjects  we  shall  study,  perhaps  we  feel 
we  know  from  our  daily  observations.  All  of  us  know 
that  water  flows  down  hill  and  not  up;  that  a  stone 
thrown  into  the  air  returns  to  the  earth  again.  Have 
we  stopped  to  learn  why  ?  To  answer  these  and  similar 
questions  is  the  work  of  science.  It  deals  with  seeking 
truths  concerning  nature. 

The  field  of  science  is  usually  sub-divided  into  the 
natural  sciences  and  the  physical  sciences.  The  natural 
sciences  deal  with  living  material,  plants  and  animals. 
To  the  study  of  plants  the  name  Botany  is  given,  to  the 
study  of  animals,  Zoology. 

The  physical  sciences  deal  with  inanimate  material  in 


A  f  EAR  IX  SCIENCE 


Definition  of  matter. 


all  its  forms  and  with  the  changes  and  processes  to  which 
it  is  subject.  Some  of  the  physical  sciences  are  Chem- 
istry, Physics,  and  Physical  Geography.  Chemistry  deals 
with  changes  in  substances  which  result  in  the  formation 
of  new  substances.  For  instance,  the  burning  of  wood 
is  a  chemical  process.  Physics  treats  of  changes  and 
processes  that  do  not  result  in  the  formation  of  other 
substances.  In  Physical  Geography  a  study  is  made  of 
weather,  climate,  and  land  forms,  and  their  relation  to 
man. 

For  the  substance  dealt  with 
in  this  general  science 
the  term  matter  is 
used.  According  to 
most  authors,  matter 
is  anything  which  oc- 
cupies space  or  has 
weight.  Thus  it  will 
be  seen  at  once  that 
wood  is  matter,  and 
that  water  is  matter. 
Matter,  however,  does 
not  exist  in  visible 
form  only,  for  gases, 
too,  are  matter. 

Is  air  matter?  An 
empty  tumbler,  that  is,  a  tumbler  which  does  not 
contain  anything  that  can  be  seen,  is  pushed  mouth 
downward  half  under  the  surface  of  the  water  in 


Fig.  1.  If  an  inverted  tumbler  is 
pushed  mouth  downward  into  water, 
the  air  within  the  tumbler  keeps  the 
water  from  entering  it. 


MATTER  3 

a  glass  jar.  The  water  rises  in  the  tumbler  only 
about  iV  of  an  inch.  Evidently  there  is  something  within 
the  tumbler  which  prevents  the  water  from  rising  to  fill 
it.  The  tumbler  is  then  tilted  sidewise  until  the  mouth 
comes  just  above  the  surface  of  the  water.  Bubbles  of 
air  escape.  If  the  tumbler  is  then  again  pushed  into  the 
water,  the  water  will  rise  into  it.  Evidently,  in  the  first 
instance^  it  was  air  that  kept  the  water  from  rising  into 
the  tumbler.  Since  the  water  rose  higher  in  the  tumbler 


Fig.  2.  A  globe  was  balanced  after  part  of  the  air  was  pumped 
from  it.  It  was  found  to  be  heavier  after  the  air  was  again  allowed 
to  enter  it. 

after  the  air  had  escaped,  this  experiment  proves  that  air 
occupies  space.  In  fact,  air  is  present  usually  in  spaces 
which  appear  empty. 

A  hollow  brass  globe  fitted  with  a  stop  cock  is  accu- 


4  A  YEAR  IN  SCIENCE 

rately  weighed.  With  an  air  pump  the  air  is  exhausted 
from  the  globe  and  the  stop  cock  is  closed.  The  globe 
is  again  weighed.  It  is  found  to  weigh  more  when  filled 
with  air  than  it  does  after  the  air  has  been  exhausted. 
Air  therefore  has  weight. 

Since  air  occupies  space  and  also  has  weight,  according 
to  the  definition  of  matter,  air  is  matter.  Air  is  a  gas,  so 
we  have  proved  that  a  gas  is  matter. 

Three  forms  of  matter.  All  material  exists  in  one 
of  three  forms :  solid,  liquid,  and  gas.  If  a  substance  has 
definite  size  and  shape,  we  call  it  a  solid.  The  shape  of  a 
solid  can  not  be  changed  except  by  some  external  force. 
If  the  size  of  a  substance  is  definite,  but  the  shape  depends 
upon  the  containing  vessel,  it  is  a  liquid.  Gases  have 
neither  definite  size  nor  shape,  and  they  expand  without 
limit. 

The  behavior  of  these  three  forms  of  matter,  and  the 
changes  which  they  undergo  under  different  conditions, 
will  be  studied  in  the  following  chapters. 

Questions 

1.  With  what  does  the  subject  of  science  deal? 

2.  Into   what   two   divisions   is   science   naturally 
divided  ? 

3.  What    is    meant    by    the    words    animate    and 
inanimate  ? 

4.  Name  the  two  natural  sciences.     How  do  they 
differ  from  each  other? 

5.  Name  three  physical  sciences.     Of  what  does 
each  treat? 


MATTER  5 

6.  State  the  definition  of  matter. 

7.  In  what  three  forms  does  matter  exist? 

8.  Define  solid,  liquid,  gas. 

9.  Name  three  solids,  three  liquids,  and  three  gases. 

10.  Is  it  possible  for  a  substance  in  the  form  of  a 
solid   to  be  changed  to   a  liquid?     To   a   gas?      Give 
examples  to  prove  your  answers. 

11.  Does  matter  exist  only  in  a  visible  form?     Give 
two  examples  illustrating  your  answer. 

12.  Why  do  gases  have  to  be  kept  in  closed  vessels? 

13.  How  can  you  prove  that  air  is  matter? 

14.  If  a  tumbler  is  filled  with  air,  how  do  you  account 
for  the  fact  that  water  can  be  poured  into  it? 

15.  State   three   reasons  why  you   think   it   is   im- 
portant for  you  to  know  something  about  science. 


CHAPTER  II 

CONSTITUTION  OF  MATTER 

Introduction.  We  have  learned  in  Chapter  I  that 
everything  in  nature,  whether  solid,  liquid,  or  gas,  is 
matter.  We  know,  too,  from  observation  that  under 
different  conditions  of  temperature  the  same  substance 
may  be  successively  a  solid,  a  liquid,  and  a  gas.  In  other 
words,  with  a  sufficiently  great  change  in  temperature 
most  substances  may  be  changed  from  one  state  of  mat- 
ter into  another.  As  an  example  take  water.  Below 
32°  F.  it  passes  into  the  solid  state ;  between  32°  F.  and 
212°  F.  it  is  a  liquid,  and  when  heated  to  212°  F.  it 
passes  into  a  vapor  or  a  gaseous  state. 

Some  common  observations.  Many  ideas .  regarding 
things  in  nature,  commonly  accepted  by  most  people 
as  self-evident,  are  found  by  scientists  to  be  entirely 
at  variance  with  the  facts.  A  glass  filled  with  water- 
is  commonly  thought  to  have  all  the  space  in  the  glass 
occupied,  yet  with  care  one  is  able  to  put  a  teaspoonful 
or  more  of  sugar  into  the  glass  without  increasing  the 
volume  of  the  water.  The  sugar  disappears  and  yet  the 
volume  of  water  does  not  increase.  A  more  striking 
phenomenon  occurs  if  fifty  cubic  centimeters  of  alcohol 
are  carefully  poured  into  a  burette  containing  fifty 


CONSTITUTION  OF  MATTER 


cubic  centimeters  of  distilled  water.  The  combined 
amounts  of  the  two  liquids  is  one  hundred  cubic  centi- 
meters. But  if  the  burette  is  closed  and  the  two  liquids 
thoroughly  mixed  there  will  be 
found  but  about  ninety-eight  cubic 
centimeters  of  the  mixture.  From 
observations  such  as  these,  scientists 
were  led  to  investigate  the  consti- 
tution of  matter.  If  a  mixture  of 
equal  quantities  of  two  substances 
is  less  than  their  combined  amounts, 
surely  the  substances  must  have 
gone  into  each  other.  To  do  this, 
however,  the  substances  must  have 
particles  and  spaces,  and  the  par- 
ticles of  one  must  have  moved  into 
the  spaces  of  the  other.  So  rea- 
soned the  early  scientists,  and  the 
result  of  their  reasoning  is  the 
"Molecular  Theory  of  Matter." 
which  explains  the  constitution  of 
matter. 

Molecular  theory.  According  to  this  theory  every- 
thing in  nature  is  composed  of  very  tiny  particles  with 
spaces  between  them.  The  particles  are  called  mole- 
cules and  the  spaces  between  the  molecules  are  called 
inter-molecular  spaces.  The  molecules  are  conceived  as 
being  in  constant  motion  back  and  forth  in  the  inter- 
molecular  spaces.  In  the  same  substance,  all  molecules 


Fig.  3.  If  water 
and  alcohol  are 
mixed,  the  two 
liquids  occupy  less 
space  than  when 
they  are  kept  sepa- 
rate. 


8 


A  YEAR  IN  SCIENCE 


are  of  equal  size,  but  they  are  of  different  sizes  in 
different  substances.  The  same  is  true  of  the  inter- 
molecular  spaces.  All  molecules  of  water  are  of  equal 
size,  but  they  differ  in  size  from  those  of  mercury. 
Molecules  are  so  small  that  they  cannot  be  seen  even 
through  the  most  powerful  microscope.  The  smallest 
particles  that  can  be  detected  with  our  best  micro- 
scopes have  a  diameter  of  1/100,000  of  an  inch.  The 

average  diameter  of  mole- 
cules has  been  computed 
by  some  authorities  to  be 
about  1/62,500,000  of  an 
inch. 

Another  statement  has 
been  made  to  the  effect 
that  if  a  cubic  inch  of 
molecules  of  air  tightly 
packed  together  could  be  so 
controlled  that  100,000,000 
of  them  could  escape  each 
second,  it  would  take  over 
100,000  years  for  all  to 
escape. 
Molecules  in  solids.  For 

Fig.  4.     Metal  ball  and  ring.         •  proof   that   Solids   are   COm- 

posed  of  molecules  we  need  only  to  recall  the  experi- 
ment of  the  ball  and  the  ring.  With  both  the  ball  and 
the  ring  at  the  same  temperature,  the  ring  just  slips 


CONSTITUTION  OF  MATTER  9 

over  the  ball,  but  when  the  ball  is  heated,  it  no  longer 
passes  through  the  ring. 

Thus  we  say,  solids  expand  with  heat  and  contract 
with  cold.  This  statement  means,  speaking  in  terms  of 
the  Molecular  Theory,  that  the  motion  of  the  molecules 
is  accelerated  by  an  increase  in  temperature  and,  mov- 
ing more  rapidly  and  with  greater  force,  they  collide, 
strike  one  another  harder,  and  rebound  from  one 
another  a  greater  distance.  The  inter-molecular  spaces 
are  thus  enlarged  and  the  Avhole  object  takes  up  more 
space. 

On  the  other  hand,  when,  heat  is  withdrawn,  the 
motion  of  the  molecules  is  retarded;  they  are  drawn 
more  closely  together,  the  inter-molecular  spaces 
become  smaller,  and  the  object  takes  up  less  space. 

Thus,  we  see  that  a  change  in  temperature  produces  a 
pronounced  change  in  the  activity  of  molecules  and 
consequently  in  the  size  of  the  inter-molecular  spaces. 

What  has  been  said  of  the  effect  of  the  change  of 
temperature  upon  solids  is  equally  true  for  most 
liquids  and  gases. 

Molecules  in  liquids.  In  liquids  the  molecules  are 
farther  apart  than  in  solids  and  have  greater  freedom 
of  movement.  This  is  shown  by  the  fact  that  liquids 
can  be  poured,  while  solids,  as  we  know,  can  not.  In 
pouring  a  liquid,  the  molecules  glide  over  each  other 
with  freedom  and  ease.  The  greater  freedom  of  mole- 
cules in  liquids  is  shown  in  diffusion.  Diffusion  is  the 


10 


A  YEAR  IN  SCIENCE 


intermingling  or  gradual  mixing  of  two  substances. 
Thus  if  two  liquids  of  different  density  or  weight  are 
placed  in  contact  with  each  other  with  the  heavier 
liquid  on  the  bottom  and  left  undis- 
turbed, it  will  be  found  in  a  few  days 
that  the  heavier  solution  is  gradually 
rising  into  the  lighter  substance.  This 
phenomenon  could  not  occur  unless 
the  substances  were  composed  of 
moving  particles  with  spaces  between. 
Solids  will  diffuse  also  if  left  in  con- 
tact with  each  other,  but  at  a  very 
much  slower  rate,  because  of  the  much 
slower  movement  of  their  molecules. 
If  a  brick  of  lead  and  a  brick  of  gold 
with  planed  surfaces  are  placed  to- 
gether, after  a  few  months  small 
particles  of  each  will  be  found  in  the 
other. 

Molecules  in  gases.  In  gases  the 
molecules  are  much  farther  apart 
than  in  solids  and  liquids,  and  consequently  they  move 
very  much  more  rapidly  than  in  either  of  the  latter. 

If  two  bottles  of  gas  of  different  density  are  placed 
mouth  to  mouth,  with  the  bottle  of  heavier  gas  on  the 
bottom,  and  left  in  that  position  for  a  few  minutes,  a 
large  portion  of  the  heavier  gas  will  be  found  in  the 
upper  bottle.  Again,  if  a  bottle  of  perfumery  is  opened 
in  a  corner  of  a  room  in  which  the  air  seems  perfectly 


Fig.  5.  If  two 
liquids  of  different 
densities  are  placed 
in  contact,  they  will 
gradually  mix. 


CONSTITUTION  OF  MATTER 


11 


still,   in   a   very  few   minutes   the   perfume   may   be 

detected  in  the  opposite  corner  of  the 

room.  Thus  gases  diffuse  very  rapidly, 

which   shows   the   great   freedom   of 

movement  of  their  molecules  within 

their  larger  inter-molecular  spaces. 

Molecules  in  different  states.  We 
have  learned  that  the  molecules  in 
gases  move  much  more  rapidly  than 
those  in  liquids,  and  the  molecules 
in  liquids  move  more  rapidly  than 
those  in  solids.  Likewise,  the  inter- 
molecular  spaces  in  gases  are  much 
larger  than  those  in  liquids  and  those 
in  liquids  are  larger  than  those  in 
solids. 

Different  sizes  of  molecules  and 
inter-molecular  spaces.  In  the  ex- 
periment already  referred  to,  in  which  50  c.c.  of 
distilled  water  were  placed  in  a  burette  and  50  c.c. 
of  alcohol  poured  carefully  on  top,  the  two  thor- 
oughly mixed  were  found  to  occupy  but  98  G.C.  The 
2  c.c.  had  not  been  lost,  but  are  accounted  for  by  the 
fact  that  the  molecules  and  inter-molecular  spaces 
of  one  liquid  are  larger  than  those  of  the  other  and  the 
smaller  molecules  of  the  one  were  crowded  into  the 
inter-molecular  spaces  of  the  other.  This  is  the  only 
way  in  which  this  phenomenon  can  be  explained. 


Fig.     6.  Carbon 

dioxide    is  heavier 

than     air,  but     it 

gradually  diffuses 

into    the  upper 
bottle. 


12  A  YEAR  IN  SCIENCE 

Questions 

1.  How  do  you  account  for  the  fact  that  you  can 
place  a  teaspooiiful  or  more  of  sugar  in  a  glass  ap- 
parently already  full  of  water,  without  causing  the 
water  to  overflow  the  sides  of  the  glass? 

2.  What    does    question    1    showT    concerning    the 
structure  of  a  liquid? 

3.  What  do  you  conclude  concerning  the  structure 
of  a  gas  after  a  liter  of  oxygen  has  been  squeezed  into 
half  a  liter  space? 

4.  What  does  the  experiment  of  the  ball  and  the 
ring  tell  .you  about  the  structure  of  a  solid  ? 

5.  What  is  a  molecule? 

6.  What  do  you  mean  by  inter-molecular  space? 

7.  Are   molecules   of  different   substances   of  the 
same  size? 

8.  Are  the  inter-molecular  spaces  in  different  sub- 
stances of  the  same  size? 

9.  Are  the  molecules  in  steam,  water,  and  ice  of 
the  same  size? 

10.  Are  the  inter-molecular  spaces  in  steam,  water, 
and  ice  of  the  same  size? 

11.  What  is  the  effect  of  an  increase  of  temperature 
on  the  molecules  of   a   substance?     Of  a   decrease   in 
temperature  ? 

12.  What  is  the  effect  of  an  increase  of  temperature 
on  the  inter-molecular  spaces   of  a  substance?     Of   a 
decrease  of  temperature? 


CHAPTER  III 
EFFECT  OF  HEAT  ON  MATTER 

Effect  of  heat  on  solids.  One  of  the  best  known 
effects  of  heat  is  the  change  which  it  causes  in  the 
size  of  a  substance.  As  stated  in  the  preceding  chapter 
a  metal  ball,  which,  when  cool,  slips  through  a  metal 
ring,  will  not  do  so  when  heated.  The  ball  increases 
in  size  when  heated.  If  the  ring  be  correspondingly 
heated,  it  becomes  so  enlarged  that  the  heated  ball  will 
pass  through  it. 

If  the  ring  is  cooled,  the  ball  will  not  pass  through  it. 
The  ring  has  decreased  in  size.  If  the  ball  is  sufficiently 
cooled,  it  will  pass  through  the  ring  as  it  did  in  the 
beginning  of  the  experiment. 

Telegraph  and  telephone  wires,  which  in  winter 
are  stretched  taut  from  pole  to  pole,  sag  in  summer, 
because  they  become  longer.  If  the  wires  were 
stretched  taut  in  the  summer,  they  would  snap  and 
break  in  the  winter,  because  there  would  not  be  suffi- 
cient slack  to  allow  them  to  contract  when  cooled. 

When  railroad  and  street  car  rails  are  laid  in  winter, 
allowance  must  be  made  for  their  expansion  in  the 
summer. 

The  tire  of  a  wagon  wheel  is  made  slightly  smaller 
than  the  wheel.  It  is  then  put  into  a  very  hot  furnace 

13 


14 


A  YEAR  IN  SCIENCE 


and  heated  until  it  expands  sufficiently  to  slip  on  the 
wheel.  When  it  cools  it  contracts,  and  then  fits  the 
wheel  closely. 

In  construction  work,  when  two  pieces  of  steel  are 
riveted  together,  the  rivets  are  used  red  hot.  When 
they  cool  they  contract  and  thus  draw  the  two  pieces 
of  steel  closer  together. 

While  we  generally  notice  the  expansion  of  a  body  in 
one  direction  only,  that  is  in  its 
length,  it  must  not  be  forgotten  that 
a  body  expands  in  three  dimensions. 

The  increase  in  length  of  a  sub- 
stance is  known  as  its  linear  expan- 
sion. The  expansion  or  contraction 
of  different  substances  is  not  equal 
for  the  same  change  in  temperature. 

If  a  bar,  made  of  two  different 
metals  tightly  welded  or  riveted  to- 
gether lengthwise,  is  heated,  it  bends. 
This  is  because  one  of  the  metals 
is  expanding  more  rapidly  than  the 
other.  If  the  bar  is  then  cooled,  it 
again  becomes  straight.  In  this  in- 
stance the  one  side  is  contracting 
faster  than  the  other. 

A  steel  wire  which  measures  ^ 
mile  on  a  cold  winter  day  will  gain  25  inches  in  length 
on  a  warm  summer  day.  Under  the  same  conditions  an 
aluminum  wire  would  gain  about  50  inches. 


Fig.  7.  A  bar 
which  is.  made  of 
two  different  met- 
als, bends  when  it 
is  heated,  because 
one  of  the  metals 
expands  more  rap- 
idly than  the  other. 


EFFECT  OF  HEAT  OX  MATTER 


15 


Effect  of  heat  on  liquids.  Not  only  are  solids  affected 
by  heat  and  cold,  but  liquids  behave  similarly  with 
changes  in  temperature.  Everyone  knows  that  if  a 
tea  kettle  is  filled  with  cold  water  and  heat  applied,  the 
water  will  soon  overflow. 

The  expansion  of  water  can  easily  be  shown  by  heat- 
ing a  test  tube  filled  with  water  and  closed 
by  a  rubber  stopper  through  which  a  piece 
of  glass  tubing  passes.     When  the 
water  is  heated  it  expands  and  rises 
in  the  small  tube.    If  the  water  in 
the  test  tube  is  cooled  by 
running  cold  water  over  it, 
the  water  in  the  tube  con- 
tracts,   falls,     and    finally 
reaches   its   original   level. 
If  mercury  is  used  in  place 
of    water,    the    expansion 
and  contraction  will  not  be 
so  great,  for  the  volume  of 
mercury   does   not   change 
so  rapidly. 

The  action  of 
a  thermometer  de- 
pends upon  the 
fact  that  mercury 
expands  when  heated  and  contracts  when  cooled.  In 
some  thermometers  alcohol  is  used  in  place  of  mercury, 
but  the  principle  involved  is  the  same. 


Fig.  8.  Experiment  to  show  the  effects 
of  a  change  of  temperature  on  the  volume 
of  a  liquid. 


16  A  YEAR  IN  SCIENCE 

An  exception  to  the  rule.  Water  shows  an  exception 
to  the  rule  that  heated  bodies  expand  and  cooled  bodies 
contract.  We  all  know  that  ice  floats.  In  order  to 
float  it  must,  of  course,  be  lighter  than  water.  Ice  is 
frozen  water,  so  evidently  in  freezing  the  water  has 
expanded.  If  two  bottles  filled  with  water  are  very 
securely  sealed,  and  then  one  is  heated  and  the  other 
allowed  to  freeze,  both  bottles  will  break.  This 
shows  that  in  each  case  the  water  has  expanded.  It 
has  been  found  that,  if  water  is  heated  above  4°C.  or 
cooled  below  that  temperature,  it  expands  in  both  cases. 

A  few  other  substances  show  a  similar  disobedience 
to  the  general  rule  for  expansion  and  contraction. 

If  water  contracted  in  freezing,  ice  would  be  heavier 
than  water  and  would  sink  in  ponds  and  lakes  as  fast 
as  it  was  formed.  As  a  result,  the  entire  pond  or 
stream  would  become  a  solid  mass  of  ice,  killing  all 
animal  and  plant  life.  It  is  a  well  known  fact  that 
even  in  the  most  severe  winter,  the  deep  lakes  do  not 
become  solid  masses  of  ice,  and  that  fish  and  some 
other  animals  remain  alive  in  the  water  beneath  the 
ice. 

Freezing  water  exerts  a  very  great  influence  on  the 
character  of  the  land  around  us.  Water  is  everywhere 
present  in  the  ground,  in  crevices,  and  even  within 
many  rocks.  When  winter  approaches  this  water 
freezes,  and  then  it  expands  about  one-eleventh  of  its 
volume.  The  rock  is  then  broken  into  countless  pieces, 
for  the  expansive  power  of  freezing  water  is  almost 


EFFECT  OF  HEAT  OX  MATTER 


IV 


irresistible.  This  effect  is  most  conspicuous  in  rocky 
or  mountainous  regions.  Here  massive  rocks  are  some- 
times pried  out  of  position,  and  large  and  small 
particles  of  rock  are  broken  off.  This  is  the  origin  of 
a  large  part  of  the  debris  brought  down  the  mountain 
slopes  by  the  spring  rains. 

Water  pipes,  in  cold  places,  are  burst  in  a  similar 
fashion.     Parts  of  cement  walks  are  sometimes   dis- 


Fig.    9.     A  solid  concrete  silo  cracked  by  uneven  contraction  and 
expansion  caused  by  extreme  cold  and  extreme  heat. 

placed,  bricks  and  even  fence  posts  are  likewise 
frequently  pushed  out  of  place  by  the  action  of  freez- 
ing water  in  the  soil. 


18 


A  YEAR  IX  SCIENCE 


The  effect  of  a  change  of  temperature  upon  gases. 

A  change  in  the  volume  of  gases  is  not  so  readily 
observed  as  it  is  in  solids  or  liquids,  because  gases  are 
invisible.  With  the  same  increase  or  decrease  in  tern- 


Fig.  10.     When  heated,  the  air  in  the  test  tube  expands  and  bubbles 
of  air  appear  in  the  water  at  the  open  end  of  the  tube. 

perature,  gases  expand  or  decrease  much  more  than 
liquids  or  solids.  This  fact  is  taken  advantage  of  in 
the  construction  of  thermometers  which  are  to  be  used 
to  register  very  slight  changes  in  temperature.  In 
such  thermometers  air  is  used. 

Automobile  and  bicycle  tires  are  not  filled  with  so 
much  air  on  a  hot  summer  day  as  they  are  on  a  cold 
winter  day.  Allowance  is  made  for  the  expansion  of 
the  air  in  the  tire. 

All   gases  expand  at  the  same  rate  for  the  same 


EFFECT  OF  HEAT  ON  MATTER  19 

increase  of  temperature,  but  the  rate  of  expansion  of 
different  liquids  and  solids  varies  considerably. 


Questions 

1.  What  effect  does  an  increase  in  temperature 
have  on  the  size  of  a  solid? 

2.  Does  a  decrease  in  temperature  have  the  same 
effect? 

3.  Why   do   telegraph   wires   which   are   taut   in 
winter  sag  in  the  summer? 

4.  If  street  car  rails  are  laid  in  the  winter  with 
the  ends  touching,  why  won't  the  cars  run  smoothly 
over  them  during  the  summer? 

5.  What  is  meant  by  linear  expansion? 

6.  Name  two  metals  which  do  not  expand  at  the 
same  rate. 

7.  With  a  change  of  temperature  do  liquids  and 
gases  behave  the  same  as  solids? 

8.  What  happens  to  a  bottle  of  milk  if  it  is  allowed 
to  freeze?    How  do  you  account  for  this  result? 

9.  If  water  did  not  expand  when  it  froze,  could 
we  use  our  present  methods  for  obtaining  the  water 
supply  for  cities?    For  removing  sewage? 

10.  Why  is  it  necessary  to  lay  water  pipes  below 
the  frost  line? 

11.  Why    does    concrete    frequently    crack    in    the 
winter  ? 

12.  Why  are  air  thermometers  sometimes  used? 


CHAPTER  IV 

TRANSFER  OF  HEAT 

Heat  may  be  transferred  from  one  substance  to 
another  in  three  different  ways:  conduction,  convec- 
tion, and  radiation.  We  shall  consider  only  the  first 
two  of  these  ways. 

Conduction.  If  one  end  of  an  iron  rod  is  held  in 
the  hand  and  the  other  end  is  placed  in  a  flame,  the 
end  held  in  the  hand  soon  becomes  hot.  Evidently  the 
heat  from  the  fire  travels  along  the  rod  from  the  flame 
to  the  hand. 

When  heat  travels  from  one  body  to  another,  with 
which  it  is  in  contact,  or  from  one  part  of  a  body  to 
another,  the  process  is  called  conduction.  Heat  flows 
from  a  warmer  to  a  cooler  part.  Coldness  is  merely 
absence  of  heat. 

A  body  which  allows  the  heat  to  travel  through  it 
is  called  a  conductor.  There  is  a  great  difference  in 
conductors,  some  being  very  good,  others  so  poor  as  to 
seem  to  allow  no  heat  to  pass  through  them.  Most 
metals  are  very  good  conductors  of  heat.  Different 
metals,  however,  vary  greatly  in  the  rapidity  with  which 
they  conduct  heat.  Copper  conducts  heat  about  four 

20 


TRANSFER  OF  HEAT  21 

times  as  rapidly  as  iron.  A  flat  iron  placed  on  a  stove 
becomes  heated  throughout;  cooking  utensils  become 
very  hot;  stoves  heat  quickly  from  the  burning  fuel 
within  them ;  etc. 

If  a  test  tube  full  of  water  is  held  in  a  flame  so  that 
the  water  boils  at  the  top,  it  will  be  some  time  before 
the  tube  will  be  hot  enough  to  pain  the  hand  by  which 
it  is  being  held.  A  bar  of  metal  of  the  same  size  would 
be  hot  before  the  tube  of 
water  even  felt  warm.  As 
compared  with  metals,  water 
is  a  poor  conductor  of  heat. 

Iron  utensils  frequently 
have  wooden  handles  because 
wood  is  a  poor  conductor  and 
does  not  allow  heat  to  pass' 
quickly  through  to  the  hand.  Fig:.  11.  when  a  test  tube 

full  of  water  is  heated  at  One 
AsbestOS  is  another  poor  COn-    end,  ^tak es  sometimejjefore 

ductor.    It  is  frequently  used  becomes  warm- 

to  wrap  hot  water  pipes  and  steam  pipes  in  order  that 

the  heat  may  not  escape. 

If  the  hand  is  placed  in  water,  which  is  the  tempera- 
ture of  the  air  around  it,  the  water  seems  much  colder 
than  the  air.  This  is  because  water  is  a  better  conductor 
than  air  and  so  takes  the  heat  out  of  the  hand  more 
rapidly. 

Fireless  cookers.  The  fireless  cooker  depends  upon 
the  principle  of  non-conduction.  One  vessel  is  placed 
inside  another.  The  space  between  the  two  is  filled 


22 


A  YEAR  IN  SCIENCE 


with  sawdust,  asbestos,  excelsior,  or  some  other  poor 
conducting  material.  Foods  are  heated  to  a  high 
temperature  and  then  placed  in  the  inner  vessel.  This 
heat  remains  in  the  food,  and  slowly  cooks  it,  because 
the  non-conducting  material  prevents  the  heat  from 
escaping. 
Explanation  of  conduction.  When  a  body  is  heated 

the  molecules  in  the  part  in  contact  with  the  heat  move 

s 


Cork 

Fig.  12.     Section  of  a  fireless  cooker ;  s}  soapstone ;  k,  kettle. 

more  rapidly.  In  their  movement  they  strike  harder 
and  faster  upon  those  next  to  them,  so  that  these  in 
turn  move  as  rapidly  as  the  first  ones.  In  this  way  the 
motion  is  carried  from  one  group  of  molecules  to 
another. 

Convection.     Notwithstanding  the  fact  that  air  and 


TRANSFER  OF  HEAT 


23 


water  are  poor  conductors,  heat  is  readily  communi- 
cated from  one  part  of  a  liquid  to  another,  or  from 
one  part  of  a  room  to  another.  The  air  in  a  cold  room 
becomes  warm  very  quickly  if  a  hot  fire  is  built. 

The  explanation  for  this  is 
simple.  When  a  liquid  or  a 
gas  is  heated,  it  expands.  The 
same  volume  of  it  will  then 
weigh  less,  and  in  conse- 
quence, it  rises.  The  cooler 
substance  around  it,  being 
heavier,  sinks  beneath  the 
lighter  part  and  forces  it  up. 
This  process  is  called  con- 
vection. 

A  kettle  of  water  on  a 
stove  is  heated  in  this  manner. 
The  water  at  the  bottom  of 


duced  in  tea  kettles  or  coffee 
pots  when  placed  over  a  fire. 
The  heated  water  expands 
and  becomes  lighter.  The 
colder  water  above  is  heavier 
and  is  drawn  down  beneath 
the  warm  water  which  in 
consequence  is  forced  upward. 


laFc?d  Vn  aVsf  tu^ulfof 
water,  a*  continuous6  current 
can  be  easily  seen  when  the 

water  is  heated. 


the  kettle  expands  and  be- 
comes lighter.  The  colder 
water  gravitates  downward, 
causing  it  to  rise.  The  colder 
water  soon  becomes  heated, 
and  in  turn  rises.  In  this 
way  all  the  water  is  soon 
heated. 

^  ^  ^^  ^"^  ***  ^ 
^Y  in  a  TOOm  becomes  heated. 
mi  .  ... 

Ihe  air  immediatelv  around 


24  A  YEAR  IN  SCIENCE 

a  radiator  or  a  register  becomes  heated  and  rises,  as 
the  colder  air  above  it  sinks  and  in  turn  becomes 
heated.  In  any  room  the  air  near  the  ceiling  is  warmer 
than  that  near  the  floor. 

Convection  due  to  displacement  of  molecules.  In 
liquids  and  gases  the  molecules  in  contact  with  the 
source  of  heat  are  set  in  violent  vibration.  These 
rapidly  vibrating  molecules  rise  and  the  cooler  ones 
then  come  in  contact  with  the  source  of  heat.  This 
process  continues  until  the  liquid  or  gas  is  uniformly 
heated  throughout. 


Questions 

1.  Name  three  ways  in  which  heat  can  be  trans- 
ferred from  one  substance  to  another. 

2.  Give  a  definition  for  conduction. 

3.  Name  two  good  conductors  of  heat.     Two  poor 
conductors. 

4.  Do  all  metals  conduct  heat  with  equal  rapidity? 

5.  From  your  observation,  how  do  solids,  liquids,  and 
gases  compare  as  conductors? 

6.  If  you  place  your  hand  on  a  piece  of  metal  or 
a  piece  of  marble,  does  it  feel  warmer  or  colder  than  a 
piece  of  wood  of  the  same  temperature?    How  do  you 
explain  this  ? 

7.  Why    are    the    pipes    leading    from    a    furnace 
wrapped  with  asbestos? 

8.  Why  are  stove  pokers  and  flat  irons  usually  pro- 
vided with  wooden  handles? 


TRANSFER  OF  HEAT  25 

9.     Will  water  at  70°  F.  feel  warm  or  cold?    Why  ? 

10.  What  is  the  structure  of  a  fireless  cooker?     Of 
a  thermos  bottle? 

11.  How  do  you  account  for  the  fact  that  a  thermos 
bottle  may  be  used  to  keep  a  liquid  either  hot  or  cold? 

12.  Why  do  we  wear  woolen  clothing  in  the  winter 
and  cotton  clothing  in  the  summer? 

13.  On  cold  nights  in  early  fall  or  late  spring,  plants 
are  sometimes  covered  with  paper.    Why  does  this  keep 
them  from  freezing? 

14.  How   does   heat   travel   through   a  substance   by 
conduction? 

15.  What  is  meant  by  convection? 

16.  Explain  how  the  water  in  a  tea  kettle  becomes 
heated  throughout. 

17.  Is  the  air  near  the  ceiling  of  a  room  warmer  or 
cooler  than  that  near  the  floor?    Why? 

18.  How    is    heat    transferred    from    a    stove    or    a 
radiator  to  all  parts  of  a  room? 

19.  How  is  any  body  cooled?    By  what  means  is  this 
usually  done  ? 


CHAPTER  V 


MEASUREMENT  OF  TEMPERATURE— 
THERMOMETRY 

Introduction.  Some  very  common  expressions  fre- 
quently heard  are,  "it's  as  cold  as  ice"  or  "it's  boiling 
hot."  Such  expressions  are  relative  and  compare  the 
temperature  of  a  substance  with  the  known  tempera- 
ture of  ice  or  boiling  water.  Thus  it  will  be  seen  that 
by  temperature  is  meant  how  hot  or  how  cold  a  given 
substance  is. 

Galileo's  thermometer.  To-day  we  are  supplied  with 
instruments  by  which  the  hotness 
or  coldness  of  a  substance  may  be 
definitely  determined.  But  such 
was  not  always  the  case.  In  fact, 
the  earliest  attempt  to  measure 
temperature  was  made  the  latter 
part  of  the  sixteenth  century 
(1592)  by  Galileo,  an  Italian 
scientist. 

His  instrument  was  known  as  the 
gas  or  air  thermometer.  •   He  had 
observed  and  knew  well  that  sub- 
stances change  in  volume  with  a 
26 


Fig.    15.     Air  thermom- 
eter made  by  Galileo. 


MEASUREMENT  OF  TEMPERATURE 


27 


c-. 


change  of  temperature.  He  knew,  too,  that  gases  respond 
far  more  rapidly  to  change  of  temperature  than  liquids 
and  solids  and  was  thus  led  to  his  air  thermometer.  This 
consisted  of  a  glass  tube  of  narrow  bore,  open  at  one 
end  and  enlarged  into  a  bulb  at  the  other.  The  open 
end  of  the  tube  was  placed  in  a  jar  of  liquid  and  the 
bulb  slightly  heated.  As  the  gas  in  the  bulb  cooled, 
the  liquid  rose  in  the  tube.  Thus  the  relative  tempera- 
ture of  the  surrounding  air  could  be  told  by  the  height 
of  the  liquid  in  the  tube. 

Mercury  thermometers;  Fahrenheit.  Early  in  the 
eighteenth  century,  1714,  Fahrenheit,  of  Danzig,  Ger- 
many, gave  to  the  world  his  mercury 
thermometer  which  is  still  used  very  ex- 
tensively throughout  the  United  States 
and  England. 

For  the  temperature  of  melting  ice  he 
marked  32°  and  that  of  boiling  water 
212°.  The  intervening  distance  he 
divided  into  180  parts  or  degrees. 

Centigrade.  In  1742  Celsius,  of  Up- 
sala,  Sweden,  devised  the  thermometer 
known  as  the  centigrade  thermometer. 
This  thermometer  is  used  almost  exclu- 
sively for  scientific  work  in  all  countries, 
and  also  for  other  purposes  in  countries 
using  the  metric  system.  As  the  word 
centigrade  (centum :  100+  gradus :  mark  CenUg?'ade6'a  n  d 

-,    N  ..  -'".,.        Fahrenheit  ther- 

or   grade)    suggests,   the   stem   of   this     mometer. 


28  A  YEAR  IN  SCIENCE 

thermometer  is  divided  into  one  hundred  equal  divisions 
between  the  freezing  and  boiling  points  of  water.  The 
freezing  point  of  water  is  marked  0°  and  the  boiling 
point  of  water  100°. 

Construction  of  centigrade  thermometer.  From  your 
examination  of  a  centigrade  thermometer  you  have 
discovered  that  it  consists  of  a  hard  glass  tube  of  vary- 
ing length,  with  a  very  fine  hair-like  opening  or  bore 
running  through  the  center.  One  end  of  the  tube  is 
blown  out  into  a  small  bulb,  filled  with  mercury,  which 
also  projects  into  the  hair-like  bore.  In  some  thermom- 
eters colored  alcohol  is  used  instead  of  mercury. 

The  other  end  of  the  tube  is  closed  and  the  stem  of 
the  tube  is  marked  for  degrees,  with  the  0°  '  marked 
freezing  and  the  100°  marked  boiling.  The  height  to 
which  the  mercury  rises  is  called  the  temperature  of 
the  given  substance.  Thus  if  mercury  in  a  centigrade 
thermometer  is  at  20  in  the  room  in  which  you  are 
sitting,  then  we  say  the  temperature  of  the  room  is 
20°C. 

Determination  of  freezing1  and  boiling  points.  To 
construct  a  thermometer  and  determine  the  essential 
points,  a  glass  tube  of  fine  bore  is  taken  and  the  bulb 
and  tube  are  filled  with  mercury  at  a  temperature 
slightly  above  the  highest  temperature  for  which  the 
thermometer  is  to  be  used.  The  open  end  of  the  tube 
is  then  sealed  off  in  a  hot  flame.  As  the  mercury  cools 
and  withdraws  from  the  tube  into  the  bulb,  it  leaves  a 
vacuum  above  it. 


MEASUREMENT  OF  TEMPERATURE 


29 


The  bulb  of  the  thermometer  is  then  surrounded 
with  melting  ice  and  left  until  the  mercury  in  the 
tube  comes  to  a  standstill.  This  point  on  the  tube  is 
marked  0°,  the  freezing  point 
of  water.  Likewise  the  bulb 
is  suspended  in  the  steam  aris- 
ing from  boiling  water  in  a 
flask  and  the  point  on  the  tube 
at  which  the  mercury  comes 
to  rest  is  marked  100°,  the 
boiling  point  of  water.  The 
intervening  distance  on  the 
tube  is  divided  into  100  equal 
parts  called  degrees.  Divi- 
sions of  the  same  length  are 


Fig.  17.  Method  of  deter- 
mining the  lower  fixed  point 
on  a  thermometer. 

extended   above    100°  C.    and 
below  0°C. 

The  Fahrenheit  thermom- 
eter is  similarly  constructed, 
with  the  freezing  point  of 
water  marked  32°  and  the 
boiling  point  of  water  212°. 
The  intervening  space  on  the 
stem  is  divided  into  180  equal 
divisions. 


Fig.  18.     Method  of  deter- 
mining the  boiling  point. 


30  A  YEAR  IN  SCIENCE 

Value  of  a  centigrade  degree  in  terms  of  Fahrenheit 
and  vice-versa.  Although  the  freezing  point  of  water 
on  the  centigrade  thermometer  is  0°,  and  on  the  Fahren- 
heit 32°,  and  the  boiling  point  of  water  on  the  centigrade 
100°,  and  on  the  Fahrenheit  212°,  it  must  be  clear  to  all 
that  the  difference  in  temperature  between  the  freezing 
and  the  boiling  points  of  water  is  the  same,  by  whatever 
thermometer  measured. 

Since  there  are  100 °C.  between  boiling  and  freezing 
and  180°  F.  (212°  boiling  —  32°  freezing  =  180°  F.) 
between  the  same  points 

100°C.  equal  180°F. 

1°C.  equals  9/5°F. 
Likewise 

180°F.  equal  100°C. 

1°F.  equals  5/9°C. 

Hence  to  reduce  from  the  centigrade  to  the  Fahren- 
heit thermometer,  multiply  the  number  of  centigrade 
degrees  by  9/5.  Then,  remembering  that  the  centi- 
grade degrees  were  measured  from  the  freezing  point, 
start  at  the  same  point  on  the  Fahrenheit  thermometer. 
If  the  temperature  is  above  freezing,  add  the  product 
to  32°.  If  below  freezing,  subtract  the  product 
from  32°. 

To  reduce  from  the  Fahrenheit  to  the  centigrade 
scale,  find  how  many  Fahrenheit  degrees  the  given 
temperature  is  above  or  below  freezing;  and  multiply 
the  number  of  degrees  by  5/9. 


MEASUREMENT  OF  TEMPERATURE  31 

Remember  always  to  make  all  computations  from 
the  same  starting  point  on  both  thermometers. 

Range  of  mercury  thermometer.  For  all  ordinary 
temperature  measurements  the  mercury  thermometer 
is  most  satisfactory.  However,  mercury  freezes  at 
— 39°C.  and  boils  at  360°C.  Alcohol  thermometers  are 
serviceable  for  temperatures  lower  than  the  freezing 
point  of  mercury,  since  the  freezing  point  of  alcohol 
is  — 130° C.  For  both  very  high  and  very  low  tem- 
peratures the  gas  thermometer  is  the  standard. 

Unit  of  heat  measure.  To  measure  anything  we  must 
have  some  measuring  unit.  For  example,  to  measure 
length,  we  have  the  foot  or  the  yard  as  a  unit.  So  to 
measure  the  amount  of  heat  a  substance  contains  it  is 
necessary  to  have  a  unit  of  heat  measure.  The  unit  here 
accepted  is  the  heat  required  to  raise  the  temperature  of 
one  gram  of  water  through  one  degree  centigrade.  This 
unit  is  called  the  (gram)  calorie.  Thus,  if  100  grams  of 
water  has  its  temperature  raised  5°C.  we  say  500  calories 
of  heat  have  passed  into  the  water ;  or  on  the  other  hand, 
if  100  grams  of  water  drops  5°C.  in  temperature,  we  say 
500  calories  of  heat  have  passed  out  of  the  water.  To 
determine  the  number  of  calories  of  heat  that  have  passed 
into  a  given  amount  of  water,  multiply  the  number  of 
grams  of  water  by  the  increase  in  degrees  centigrade. 
The  result  will  be  in  calories. 


32  A  YEAR  IN  SCIENCE 

Questions 

1.  Who  was  Galileo  ?    Tell  something  of  his  work. 

2.  What  is  temperature  and  how  is  it  measured  ? 

3.  State  the  principle  upon  which  the  thermometer 
is  based. 

4.  Give  several  reasons  why  mercury  is  the  most 
satisfactory  of  all  known  substances  for  use  in  ordinary 
thermometers. 

5.  Would  the  range  of  a  mercurial  thermometer  of 
given  length  be  increased  or  decreased  by  reducing  the 
size   of  the  bulb?     By  making  the  bore  of  the  tube 
smaller?    Would  the  distance  representing  a  degree  be 
increased  or  decreased? 

6.  How  would  the  readings  of  a  thermometer  be 
affected  if  the  bulb  should  contract  after  the  gradua- 
tions had  been  made? 

.7.     How  would  you  proceed  to  test  experimentally 
the  points  on  a  mercurial  thermometer  ? 

8.  The  following  temperature  measurements  were 
taken  with  a  Fahrenheit  thermometer:     77°,  41°,  14°, 
—4°,  — 40°.     What  would  a  centigrade  thermometer 
have  indicated? 

9.  The  difference  in  temperature  between  two  ves- 
sels of  water  is  35°  C.     What  is  the  difference  in  F. 
reading  ? 

10.  A  100  g.  mass  of  copper  rises  in  temperature 
from  15°  C.  to  100°  C.    How  much  heat  does  it  absorb? 

11.  Who  was  Fahrenheit? 

12.  Do  you  know  why  he  established  32°   on  his 
thermometer  as  the  freezing  point  and  212°  as  the  boil- 
ing point  of  water? 

13.  Who  was  Celsius? 

14.  What  is  the  meaning  of  centigrade  ? 


MEASUREMENT  OF  TEMPERATURE  33 

15.  Which    of    the    two    thermometers    should    be 
adopted  for  general  use?    Why? 

16.  How  is  a  thermometer  made? 

17.  How  are  the  essential  points  of  freezing  and 
boiling  determined? 

18.  What    is   the    freezing    point    of    mercury?     Of 
alcohol  ? 

19.  Why  is  a  heat  unit  necessary  ? 

20.  What  is  the  name  of  the  heat  unit  used  ? 

21.  How  much  heat  does  this  unit  represent .' 

22.  One  gram  of  water  has  its  temperature  raised 
20°  C.    How  many  calories  of  heat  were  used? 

23.  The   temperature  of  fifty  grams  of  water  was 
raised  1°  C.    How  many  calories  of  heat  were  used  ? 

24.  How  many  calories  of  heat  are  required  to  raise 
the  temperature  of  15  grams  of  water  from  10°  C.  to  18° 
C.?    From  32°  F.  to  50°  F.f 


CHAPTER  VI 

CHANGES  IN  STATE  OF  MATTER 

Three  states  of  matter.  It  is  a  familiar  fact  that 
water  may  exist  in  three  different  forms.  It  may  be  a 
solid,  a  liquid,  or  a  gas.  When  a  solid  it  is  called  ice; 
when  a  liquid,  water;  and  when  a  gas,  steam. 

It  is  not  so  well  known  that  many  other  substances 
also  exist  in  three  forms.  The  chief  reason  for  this 
lack  of  knowledge  is  the  fact  that  few  substances  are 
as  useful  as  water,  in  all  three  forms  in  which  they 
exist.  Few  substances,  therefore,  have  been  studied 
as  carefully  as  water. 

Most  of  us  know  many  substances  which  exist  both 
as  solids  and  as  liquids.  Iron  and  lead  we  know  can  be 
melted ;  paraffin  can  easily  be  melted  and  thus  changed 
from  the  solid  to  the  liquid  state.  Many  substances 
require  extremely  high  or  extremely  low  temperature 
to  change  from  one  of  these  states  to  another.  Most 
metals,  for  instance,  assume  the  gaseous  state  only  at 
very  high  temperature,  and  many  common  gases 
become  liquid  and  solid  only  at  very  low  temperature. 
Air  has  been  known  in  the  liquid  and  the  solid  states 
only  within  the  last  twenty-five  years. 

So  far  as  is  known,  all  substances  become  solids  when 

34 


CHANGES  IX  STATE  OF  MATTER         35 

sufficiently  cooled.  Some  change  directly  from  gases 
into  solids,  or  solids  into  gases,  without  assuming  the 
intermediate  liquid  state.  For  instance,  when  crystals, 
of  iodine  are  heated  they  pass  directly  into  the  gaseous 
state.  On  a  cold  winter  day,  snow  or  ice  on  a  cement 
walk  will  disappear  and  yet  the  walk  has  not  been 
wet  at  all.  The  snow  or  ice  passed  from  the  solid  to 
the  gaseous  state  without  becoming  water.  This  water 
vapor  may  then  pass  directly  back  to  the  solid  from  the 
gaseous  state;  as,  for  instance,  when  snow  and  frost 
are  formed.  It  is  impossible  to  convert  some  solids 
into  liquids,  because  if  heated  beyond  a  certain  tem- 
perature they  burn.  Wood  and  paper,  for  example, 
do  not  become  liquid  when  heated. 

Change  from  solid  to  liquid,  and  liquid  to  gas. 
Changes  in  the  state  of  matter  are  most  readily  brought 
about  by  changes  in  temperature.  In  raising  a  body 
from  a  lower  to  a  higher  temperature,  heat  is  consumed. 
For  instance,  heat  is  consumed  in  raising  100  c.c.  of 
water  from  25°  C.  to  35 °C.,  or  in  raising  ice  from 
_10°C.  to  — 2°C. 

Heat,  however,  is  also  consumed  in  changing  a  solid 
to  a  liquid  or  a  liquid  to  a  gas.  If  ice  at  — 10° C.  is 
slowly  heated,  a  thermometer,  imbedded  in  the  ice, 
will  show  a  gradual  rise  in  temperature  until  0°C.  is 
reached.  Then  for  some  time  the  thermometer  will 
show  no.  rise  in  temperature.  During  this  time  the  ice 
is  melting. 

As  soon  as  the  ice  has  melted,  the  rise  in  temperature 


36 


A  YEAR  IN  SCIENCE 


begins  again.  This  rise  continues  until  a  temperature 
of  100° C.  is  reached.  Then  the  mercury  in  the  ther- 
mometer again  becomes  stationary.  This  time  the 


Fig.  19.  When  water  is  heated  it  changes  to  a  gas,  which  as  it 
escapes,  forms  bubbles  in  the  water.  This  water  vapor  is  transpar- 
ent when  it  is,  in  the  flask,  and  also  where  it  issues  from  the  end 
of  the  tube.  As  soon  as  it  cools^  it  again  condenses  in  the  form 
of  steam. 

water  is  being  changed  into  steam.  When  the  water 
has  all  been  converted  into  steam,  the  mercury  again 
rises,  provided  the  steam  is  in  a  vessel  from  which  it 
can  not  escape. 


CHANGES  IN  STATE  OF  MATTER  37 

Since  the  temperature  of  the  ice  when  it  begins 
melting  is  0CC.,  and  since  the  temperature  of  water 
immediately  after  melting  is  0°C.,  it  is  evident  that 
the  heat  has  not  caused  an  increase  in  the  temperature 
of  the  water.  It  is  thus  clear  that  all  the  heat  must 
have  been  used  in  effecting  the  change  of  state  from 
solid  ice  to  water. 

Since  the  temperature  of  the  water  just  before  it 
changes  into  steam  is  the  same  as  it  is  after  it  has  all 
become  steam,  the  heat  must  be  consumed  in  the  change 
from  water  to  steam. 

Quantity  of  heat  necessary  to  change  ice  to  water. 
Heat  is  necessary  to  change  ice  to  water.  In  order  to 
determine  the  amount  of  heat  necessary  for  this  pur- 
pose, the  experiment  must  be  conducted  so  that  all  the 
heat  used  will  be  consumed  solely  for  melting  the  ice. 

From  a  number  of  experiments  it  has  been  learned 
that  it  requires  about  80  calories  of  heat  to  change  1 
gram  of  ice  to  water.  (See  Laboratory  Manual,  Exercise 
15.)  Heat  must  then  be  applied  to  ice  to  melt  it. 

We  have  learned  that  it  takes  heat  to  melt  ice,  or  to 
change  it  to  water.  In  the  laboratory  the  source  of  this 
heat  is  the  Bunsen  burner,  or  some  other  artificial 
means.  However,  when  ice  melts  on  exposure  to  the 
air,  or  without  any  special  attempt  being  made  to 
apply  heat  to  the  ice,  the  fact  that  a  considerable  quan- 
tity of  heat  is  required  to  melt  it  is  often  overlooked. 
The  source  of  heat  in  this  case  is  from  the  air  itself 
and  from  the  surrounding  objects. 


38  A  YEAR  IN  SCIENCE 

The  fact  that  ice  in  melting  withdraws  heat  from  the 
surrounding  objects  is  of  value  in  many  ways.  The  ice 
in  an  ice  chest,  in  melting,  takes  heat  from  the  food 
placed  in  the  chest.  When  snow  melts  in  the  spring  it 
cools  the  air,  and  thus  prevents  the  very  rapid  melting 
of  snow  which  might  otherwise  cause  floods. 

Heat  necessary  to  dissolve  a  substance.  If  a  handful 
of  salt  is  placed  in  a  glass  full  of  water  and  very  slowly 
stirred  with  a  thermometer,  the  temperature  gradually 
decreases  as  the  salt  dissolves.  The  salt  is  changing 
from  a  solid  to  what  may  be  considered  a  liquid.  In 
order  to  do  this  heat  is  necessary.  In  this  experiment, 
the  heat  comes  from  the  water. 

In  ice  cream  freezers  the  chopped  ice  is  mixed  with 
coarse  salt.  Heat  is  taken  from  the  cream  not  only  to 
melt  the  ice  but  also  to  dissolve  the  salt.  As  a  result 
the  cream  freezes.  The  mixture  of  salt  and  wrater  does 
not  freeze  because  its  freezing  point  is  below  that  of 
pure  water. 

Heat  given  off  when  liquids  become  solids.  A  flask 
in  which  50  grams  of  sodium  hyposulphite  and  10  c.c.  of 
water  have  been  placed  is  heated  slowly  until  all  the 
sodium  hyposulphite  is  dissolved.  The  flask  is  then 
removed  from  the  flame,  closed  with  a  plug  of  cotton,  and 
very  carefully  set  aside  to  cool.  Care  should  be  taken 
that  the  flask  and  its  contents  are  not  disturbed  for  about 
forty  minutes.  If  the  cotton  plug  is  then  removed,  and  a 
thermometer  is  placed  in  the  liquid,  the  solution  at 
once  begins  to  crystallize.  The  hypo  changes  from 


CHANGES  IN  STATE  OF  MATTER  39 

the  liquid  state  to  the  solid.  As  this  change  is  taking 
place  the  temperature  gradually  rises,  as  is  indicated 
on  the  thermometer. 

When  a  liquid  changes  to  a  solid,  heat  is  given  off 
or  liberated.  The  amount  of  heat  given  off  is  equal 
to  the  amount  consumed  in  changing  the  substance 
from  a  solid  to  a  liquid.  For  example,  the  amount  of 
heat  lost  by  freezing  water  is  exactly  equal  to  the 
amount  of  heat  absorbed  by  melting  ice. 

The  temperature  of  the  atmosphere  near  a  lake  or 
river  in  which  the  water  is  freezing,  is  higher  than  that 
of  the  surrounding  atmosphere  because  of  the  heat 
given  off  by  the  freezing  water.  When  the  water  at 
the  surface  of  a  lake  or  river  freezes,  it  gives  out  its 
heat  to  the  air  immediately  above.  Ice  and  water  are 
both  poor  conductors  of  heat,  and  the  layer  of  ice  once 
formed  over  the  surface  prevents  the  underlying  water 
from  giving  off  any  more  heat.  This  causes  the  freez- 
ing to  be  very  slow.  It  also  accounts  for  the  compara- 
tively slight  depth  to  which  the  water  freezes. 

Farmers  sometimes  make  use  of  this  fact  by  placing 
in  their  cellars  tubs  of  water,  which,  as  it  freezes,  gives 
out  heat  and  thus  prevents  vegetables  from  freezing. 
Fortunately,  most  winter  vegetables  do  not  suffer  from 
cold  until  a  temperature  of  several  degrees  below  the 
freezing  point  is  reached. 

Melting*  points.  At  ordinary  pressure  of  the  air, 
i°e  melts  at  0°C.  This  temperature  is  known  as  the 
meltina  voint  of  ice.  Other  substances  do  not  melt  at 


40  A  YEAR  IN  SCIENCE 

this  temperature,  but  each  has  its  own  melting  point. 
For  instance,  alcohol  melts  at  — 130°  C.,  mercury  at 
— 39.5°C.,  zinc  at  419°C.,  copper  at  1065°C.,  and  cast 
iron  at  1200°C. 

The  melting  temperatures  of  some  substances,  espe- 
cially gases,  are  so  low  that  they  have  never  been  seen 
in  the  solid  state  outside  of  the  laboratory,  or  in  the 
liquid  state  except  in  laboratories  where  very  low  tem- 
peratures can  be  artificially  produced. 

The  fact  that  the  melting  points  of  substances  differ 
greatly  makes  it  possible  to  melt  sugar  in  a  glass  vessel, 
or  glass  in  an  iron  vessel.  Why? 

Some  substances  gradually  soften  and  become  pliable 
before  they  melt.  This  fact  is  utilized  in  the  molding 
of  glass  or  iron  into  different  forms. 

Boiling1  points.  The  temperature  at  which  a  liquid 
becomes  a  gas  is  known  as  its  boiling  point.  The  boiling 
point  of  a  substance  is  also  the  temperature  at  which, 
in  a  gaseous  state,  it  condenses  and  again  becomes  a 
liquid.  For  instance,  water  boils  at  100° C.  Steam  also 
condenses  at  this  temperature. 

Liquids  have  their  characteristic  boiling  points  just 
as  solids  have  their  characteristic  melting  points.  The 
boiling  point  of  ether  is  35°C.,  of  alcohol  78°C.,  of 
water  100°C.,  of  mercury  350°C.,  of  sulphur  448°C.,  of 
zinc  1040°C.,  and  of  copper  2100°C. 

Some  substances  boil  at  very  low  temperatures. 
Most  of  those  substances  are  never  seen  in  the  liquid 
state,  except  in  laboratories.  They  are  known  only  in 


CHANGES  IN  STATE  OF  MATTER 


41 


the  form  of  gases.     Such  gases  are  hydrogen,  oxygen, 
and  carbon  dioxide. 

Distillation.  The  fact  that  different  liquids  boil  at 
different  temperatures  is  utilized  in  the  separation  of 
various  substances  by  means  of  a  process  known  as 
distillation.  If  a  mixture  of  alcohol  and  water  is  heated 
between  78°C.  and  100°C.  the  alcohol  will  boil  and 
pass  off  as  a  vapor,  while 
the  water  will  remain.  If 
the  alcohol  vapor  is  then 
cooled,  it  will  again  become 
a  liquid.  If  the  boiling 
points  of  the  two  liquids  lie 
close  together,  as  they  do 
in  this  case,  repeated  dis- 
tillation is  necessary.  Even 
then  a  complete  separation 
can  not  be  obtained  by  dis- 
tillation alone. 

Commerciallv.  distillation 


Fig.  20.  Distillation.  The  solu- 
tion to  be  distilled  is  placed  in 
the  flask.  The  steam  passes 
through  the  tube,  is  cooled,  and 
condenses  in  the  test  tube.  Any 
impurities  present  in  the  original 
liquid  are  left  in  the  flask. 


is  a  very  important  process. 
When  liquids  contain  dis- 
solved solids,  the  liquids 
can  usually  be  distilled.  Water  can  be  freed  from  impur- 
ities by  it.  If  muddy  water  is  boiled,  the  water 
evaporates,  or  passes  off  in  the  form  of  steam,  but  the 
impurities  remain  in  the  vessel  in  which  the  water  is 
being  boiled.  The  steam  can  then  be  condensed  and  pure 
water  obtained.  Water  freed  from  impurities  in  this  way 


42 


A  YEAR  IN  SCIENCE 


is  called  distilled  water,  and  the  process  is  called  distilla- 
tion. By  this  method,  the  salt  water  of  the  ocean  may  be 
separated  into  pure  drinking  water  and  salt.  Distilled 
water  is  used  by  chemists  in  their  work ;  it  is  used  in  the 
manufacture  of  artificial  ice  and  also  for  drinking  water. 

Turpentine  is  made  by  distilling  the  sap  of  pine 
trees.  The  sap  is  collected  and  heated.  Turpentine 
passes  off  as  a  steam,  and  rosin  is  the  mass  left  in  the 
boiler. 

Effect  of  change  of  pressure  on  boiling  point.  Water 
is  placed  in  a  flask  and  heated  to  about  70° C.  A  ther- 
mometer is  then  put  in  the  flask;  the  whole  apparatus 
is  placed  under  the  receiver  of  an  air  pump,  and  the 


Fig.  21.  If  part  of  the  air  is  withdrawn  by  means  of  an  air 
pump  from  around  the  flask,  water  in  the  flask  will  boil  at  a  tem- 
perature far  below  100  °C. 

air  is  exhausted.  When  the  pressure  is  sufficiently 
diminished  the  water  boils  violently  at  a  temperature 
far  below  the  usual  boiling  point. 


CHANGES  IN  STATE  OF  MATTER 


43 


Water  is  boiled  in  a  flask  until  the  air  has  been 
expelled  by  the  steam.  It  is  then  quickly  closed  with 
a  tight  cork  and  inverted.  If  cold  water  is  then 
poured  over  the  flask,  the  water  within  it  boils  vio- 
lently. The  cold 
water  condenses  some 
of  the  steam  in  the 
flask,  thereby  dimin- 
ishing the  pressure 
in  the  flask,  and  as 
a  result  the  water 
boils. 

From  these  experi- 
ments we  learn  that 
the  boiling  point  of 
water  is  lowered  if 
the  pressure  is  dimin- 
ished. 

T)^~  ~f    +1, «    j:          Fig.    22.      Water    is    boiling    in    the 

Because    Ot    the    dl-  flask  while  cold  water  is  being  poured 
.     .   ,      ,  ,  over   it 

mmished  atmospheric 

pressure  at  high  altitudes,  the  boiling  point  of  a  liquid 
is  considerably  lower  upon  a  mountain  than  it  is 
near  sea  level.  On  Pike's  Peak  water  boils  at 
about  86°C. 

On  the  other  hand,  experiments  have  shown  that 
water  will  not  boil  even  at  a  temperature  of  100 °C., 
if  the  pressure  is  increased  above  normal  at  sea  level. 

A  change  in  pressure  also  affects  the  melting  points 
of  substances.  A  decrease  in  pressure  will  usually 


44  A  YEAR  IN  SCIENCE 

raise  the  melting  point,  and  an  increase  in  pressure 
will  usually  lower  the  melting  point. 

Quantity  of  heat  used  in  changing  water  to  steam. 
The  quantity  of  heat  necessary  to  change  1  c.c.  of 
water  into  water  vapor,  or  steam,  can  be  determined. 
(See  Laboratory  Manual,  Exercise  18.)  Experiments 
have  proved  that  it  takes  about  536  calories  of  heat  to 
convert  1  c.c.  of  water  into  vapor.  This  is  about  5J  times 
as  much  heat  as  is  necessary  to  raise  the  same  amount  of 
water  from  0°  to  100° C. 

Heat  withdrawn  in  evaporation  of  liquids.  If  chloro- 
form or  ether  is  left  exposed  to  the  air  it  evaporates 
very  rapidly.  Likewise,  if  water  is  left  exposed  to 
the  air  it  evaporates.  The  liquids,  which  have  appar- 
ently disappeared,  have  passed  into  the  surrounding 
air  in  the  form  of  vapor.  When  water  is  converted 
into  vapor  by  ordinary  evaporation,  heat  is  consumed 
in  the  same  manner  as  when  Avater  is  converted  into 
steam  by  boiling,  but  the  process  is  very  much  slower. 
The  heat,  which  is  used  in  evaporation,  is  withdrawn 
from  the  surrounding  objects. 

Evaporation  is  a  slow  process,  occurring  at  all  tem- 
peratures. It  is  hastened  in  the  summer  because  of 
the  large  amount  of  heat  in  the  atmosphere. 

After  a  shower  of  rain,  the  water  evaporates  and 
cools  the  air.  When  streets  are  sprinkled,  the  water 
not  only  lays  the  dust,  but  in  evaporating  cools  the 
atmosphere.  When  perspiration  evaporates  from  the 
skin  it  cools  the  surface  of  the  body.  In  tropical 


C'HAXOE*  IX  STATE  OF  MATTER 


countries  water  is  cooled  by  being  placed  in  porous 
jars.  A  small  quantity  of  water  passes  through  the 
pores  of  the  jar,  and, 
on  evaporating,  with- 
draws enough  heat 
from  the  water  re- 
maining in  the  jar  to 
cool  it. 

Artificial  ice.  This 
same  principle  is  util- 
ized in  the  manufac- 
ture of  artificial  ice. 
In  countries  where  it 
is  never  cold  enough 
to  freeze  the  water  in 
ponds,  all  the  ice 
formerly  used  had 
to  be  shipped  from 
colder  countries.  Of 
late  years,  however, 
men  have  devised 
methods  by  which  ice 
may  be  made  very 
cheaply  even  in  the  warmest  places.  In  fact,  these 
methods  offer  so  many  advantages,  that  even  in  our 
northern  cities  great  quantities  of  artificial  ice  are  used. 

The  method  most  commonly  used  in  the  artificial 
production  of  ice  is  known  as  the  ammonia  method. 
This  depends  upon  the  fact  that  pure  ammonia,  which 


Copyright  by  Henry  G.  Pedbody. 

Fig.  23.     An  Indian  woman  carrying 

an  olla,  a  porous  water  jug,  in  which 

the  water  is  cooled  by  the  evaporation 

of  water  from  the  outside  of  the  olla. 


46  A  YEAR  IN  SCIENCE 

is  a  gas,  may  be  condensed  into  a  liquid  form  by  great 
pressure,  and  as  soon  as  the  pressure  is  removed  the 


Fig-.  24.  Interior  of  tank  room  in  ice  factory.  The  brine  tank 
and  the  ammonia  coils  are  under  the  floor.  Two  cans  ready  to  be 
filled  with  distilled  water  are  shown  at  the  right. 

liquid  quickly  changes  into  a  gas  again,  the  rapid 
change  requiring  much  heat. 

Ammonia  gas  is  liquefied  by  strong  pressure  and  low 
temperature.  It  is  then  allowed  to  flow  into  pipes 
which  run  through  tanks  containing  salt  water.  As 
soon  as  the  pressure  is  reduced,  the  liquid  ammonia 
evaporates  and  becomes  a  gas.  In  doing  this  it  with- 
draws heat  from  the  salt  water,  reducing  its  tempera- 
ture far  below  the  freezing  temperature  of  pure  water. 
Immersed  in  the  salt  water  are  molds  containing  pure 
water.  The  water  in  the  molds  freezes  and  is  with- 
drawn as  solid  cakes  of  ice. 

Heat  given  off  in  condensation.  If  a  glass  plate  is 
held  over  boiling  water,  drops  of  water  collect  on  it. 
The  steam  is  cooled  on  coming  in  contact  with  the  glass 


CHANGES  IX  STATE  OF  MATTER  47 

plate  and  condenses  into  water.  In  winter,  steam  col- 
lects on  the  window  panes,  if  the  room  is  warm  and 
the  air  is  moist.  A  pitcher  of  ice  water  when  standing 
in  a  warm  room  becomes  covered  with  drops  of  water. 
When  the  moisture  in  the  air  comes  in  contact  with 
the  cold  surface,  it  immediately  condenses. 

When  steam  condenses  into  water,  heat  is  released. 
The  amount  of  heat  thus  liberated  is  equal  to  the 
amount  of  heat  used  in  transforming  the  water  into 
steam.  In  other  words,  it  requires  536  calories  of  heat 
to  convert  1  gram  of  water  into  steam,  and  1  gram 
of  steam  gives  off  536  calories  of  heat  during  its  con- 
densation into  water. 

The  liberation  of  heat  by  condensation  is  made  use 
of  in  the  system  of  steam  heating.  Water  is  boiled  in 
a  boiler,  and  a  large  amount  of  heat  is  used  to  convert 
the  water  into  steam.  The  steam  passes  through  pipes 
which  run  to  the  radiators  in  various  parts  of  the 
building.  There  the  steam  condenses  and  in  so  doing 
liberates  large  quantities  of  heat,  thereby  giving  up 
to  the  air  of  the  room  much  of  the  heat  which  it  had 
absorbed  from  the  fire. 

Change  in  volume  resulting  from  change  in  state. 
A  change  in  the  form  of  a.  substance,  from  a  solid  to 
a  liquid,  for  example,  is  invariably  accompanied  by  a 
change  of  volume. 

With  the  exception  of  ice,  most  solids  expand  on 
becoming  liquids,  and  liquids  expand  when  they 
become  gases.  The  volume  of  water  is  greatly 


48  A  YEAR  IN  SCIENCE 

increased  when  it  becomes  steam.  All  of  us  know  of 
the  force  exerted  by  steam.  This  enormous  force  is 
utilized  in  all  the  numerous  kinds  of  steam  engines. 

The  return  from  the  gaseous  to  the  liquid  state,  or 
from  the  liquid  to  the  solid  state,  is  always  accom- 
panied by  a  considerable  decrease  in  volume. 

Molecular  changes  resulting  from  change  in  state. 
We  already  know  that  if  the  temperature  of  a  solid  is 
increased,  its  volume  is  also  increased.  We  also  know 
that  this  is  because  the  molecules  of  the  solid  have 
been  driven  farther  apart.  By  continuous  heating, 
the  molecules  of  a  solid  may  be  driven,  or  forced,  far 
enough  apart  actually  to  change  the  form  of  the  sub- 
stance from  that  of  a  solid  to  that  of  a  liquid.  Simi- 
larly, when  the  molecules  of  a  liquid  are  forced  far 
enough  apart,  the  liquid  becomes  a  gas. 

Anything  which  interferes  with  the  free  movement 
of  the  molecules  will  increase  the  amount  of  heat  neces- 
sary to  change,  for  example,  a  liquid  to  a  gas.  Conse- 
quently, if  the  air  pressure  on  a  liquid  is  increased, 
its  boiling  point  is  raised.  The  reverse  is  also  true, 
that  if  the  pressure  upon  a  liquid  is  reduced,  the  mole- 
cules can  move  apart  more  readily,  and  consequently, 
less  heat  is  necessary  to  convert  the  liquid  into  a  gas. 

We  thus  see  that  by  decreasing  the  pressure  upon 
solids  or  liquids,  less  heat  is  necessary  to  change  them 
into  gases. 

It  is  also  true  that  to  change  a  gas  to  a  liquid,  or  a 
liquid  to  a  solid,  the  molecules  must  be  brought  closer 


CHANGES  IN  STATE  OF  MATTER  49 

together.  This  can  be  brought  about  in  two  ways: 
first,  by  reducing  the  temperature  of  the  substances, 
and  second,  by  increasing  the  pressure  upon  them. 

It  is  only  by  the  combination  of  a  great  increase  in 
pressure  and  a  great  decrease  in  temperature,  that  it 
has  been  possible  to  convert  some  gases  into  liquids, 
and  the  resulting  liquids  into  the  solid  state. 

Questions 

1.  In  what  three  forms  may  a  substance  exist  ? 

2.  Name  two  solids  which  cannot  be  changed  to 
liquids.     Why  is  it  impossible  to  convert  them  into 
liquids  ? 

3.  At  what  temperature  does  water  boil?    Freeze? 

4.  How   many   calories    of   heat   are    required   to 
change  one  gram  of  ice  to  water? 

5.  What  are  the  sources  of  heat  for  melting  ice 
in  a  refrigerator? 

6.  Is  it  warmer  or  cooler  near  a  body  'of  melting 
ice  than  it  is  at  some  distance  away?    Why? 

7.  Why  is  salt  mixed  with  chopped  ice  for  use  in 
ice  cream  freezers? 

8.  What  effect  does  water  which  is  melting  have 
upon  the  surrounding  temperature  ? 

9.  How  many  calories  of  heat  are  given  off  when 
10  grams  of  water  are  changed  to  ice  ? 

10.  What  is  the  melting  point  of  ice?     Alcohol? 
Mercury  ? 

11.  Why  is  it  impossible  to  melt  iron  in  a   glass 
dish? 

12.  What  is  the  boiling  point  of  water?     Alcohol? 
Ether?    Mercury?    Copper? 


50  A  YEAR  IN  SCIENCE 

13.  What  is  meant  by  distillation? 

14.  State   several   ways   in   which   the   process    of 
distillation  is  of  commercial  value. 

15.  Why  is  it  impossible  to  cook  potatoes,  by  boil- 
ing, on  top  of  Pike's  Peak? 

16.  How   many   calories    of   heat   are   required   to 
change  one  cubic  centimeter  of  water  into  steam? 

17.  Why  is  it  cooler  after  the  streets  have  been 
sprinkled  ? 

18.  How  does  perspiration  cool  the  body? 

19.  What  is  the  method  used  in  the  production  of 
artificial  ice? 

20.  Why  can  you  see  your  breath  on  a  cold  winter 
day? 

21.  Explain  how  heat  is  transferred  by  means  of 
steam  from  the   coal  burning  in  the  furnace  to  the 
rooms  of  a  house. 

22.  What  change  takes  place  in  the  volume  of  a 
substance  when  it  changes  from  a  solid  to  a  liquid?    A 
liquid  to  gas  ?    A  gas  to  a  liquid,  or  a  liquid  to  a  solid  ? 


CHAPTER  VII 

PHYSICAL  AND  CHEMICAL  CHANGES 

Physical  change.  Matter  may  undergo  many 
changes.  One  class  of  these  changes  is  not  accom- 
panied by  any  alteration  in  the  composition  of  matter. 
When  a  piece  of  glass  is  broken  the  small  pieces  do 
not  differ  from  the  original  piece  except  in  size.  A 
piece  of  iron  may  be  broken,  it  may  be  magnetized, 
it  may  be  heated,  it  may  be  melted,  and  it  may  be 
converted  into  a  vapor.  In  none  of  these  changes,  how- 
ever, has  the  composition  of  the  iron  been  affected. 
The  pieces  of  iron,  the  magnetized  iron,  the  heated 
iron,  the  melted  iron,  or  the  iron  vapor  are  just  as 
truly  iron  as  was  the  original  piece.  Sugar  may  be 
dissolved  in  water,  but  neither  the  sugar  nor  the  water 
is  changed  in  composition.  The  resulting  liquid  has 
the  sweet  taste  of  sugar,  but  the  water  can  be  evap- 
orated by  heating  and  the  sugar  recovered  unchanged. 
Such  changes  are  called  physical  changes.  Physical 
changes  are  those  which  do  not  involve  a  change  in  the 
composition  of  substances.  In  other  words,  a  physical 
change  is  a  change  in  the  form  but  not  in  the  nature 
of  a  substance. 

51 


52  A  YEAR  IN  SCIENCE 

Chemical  change.  Matter  may  undergo  other 
changes  in  which  it&  composition  is  altered.  When  a 
piece  of  coal  is  burned,  ashes  and  invisible  gases  are 
formed.  These  are  entirely  different  in  composition 
and  properties  from  the  original  coal.  Iron  when 
exposed  to  moist  air  is  gradually  changed  into  rust. 
This  rust  is  not  the  same  as  the  iron.  If  sugar  is  cov- 
ered with  sulphuric  acid  and  slowly  heated,  a  black 
substance  is  formed  which  is  neither  sweet  nor  soluble 
in  water.  Such  changes  are  evidently  quite  different 
from  the  physical  changes  just  described,  for  in  them 
new  substances  are  formed  in  place  of  the  ones  under- 
going change.  Changes  of  this  kind  are  called 
chemical  changes.  Chemical  changes  are  those  which 
involve  a  change  in  the  composition  of  substances  and 
result  in  the  formation  of  new  substances. 

Questions 

1.  What  is  a  physical  change? 

2.  Name  three  physical  changes. 

3.  How    does    a    chemical    change    differ    from    a 
physical  change? 

4.  Name  three  chemical  changes. 

5.  Classify  the  following  as  examples  of  physical 
or  chemical  changes : 

a.  Ice  to  water. 

b.  Hydrochloric  acid  on  marble. 

c.  Burning  of  wood. 

d.  Carbon  dioxide  in  lime  water. 

e.  Electric  current  passing  over  a  wire. 


CHAPTER  VIII 

CHEMICAL  PHENOMENA 

Physical  and  chemical  properties.  Many  so-called 
properties  of  a  substance  can  be  noted  without  causing 
the  substance  to  undergo  chemical  change,  and  are  there- 
fore called  its  pliysical  properties.  Among  these  are  its 
physical  state,  color,  odor,  taste,  size,  shape,  and  weight. 

Other  properties  are  discovered  only  when  a  substance 
undergoes  chemical  change.  These  are  called  its  chemical 
properties.  We  know,  for  example,  that  wood  burns  in 
air ;  that  carbon  dioxide  turns  lime  water  milky ;  and  that 
iron  rusts  when  exposed  to  the  air. 

Classification  of  matter.  At  first  sight  there  appears 
to  be  no  limit  to  the  varieties  of  matter  of  which  the 
world  is  made.  For  convenience  in  study  we  may 
classify  all  these  varieties  under  three  heads;  namely: 
mechanical  mixtures,  chemical  comppunds,  and 
elements. 

Mechanical  mixtures.  If  equal  amounts  of  salt  and 
iron  filings  are  thoroughly  mixed  together,  the  result- 
ing product  has  the  appearance  of  a  new  substance. 
If  it  is  examined  more  closely,  however,  it  will  be  seen 
to  be  merely  a  mixture  of  salt  and  iron,  each  of  which 

53 


54 


A  YEAR  IN  SCIENCE 


substances  retains  its  own  peculiar  properties.  The 
particles  of  salt  and  the  particles  of  iron  can  be  easily 
detected.  A  magnet  held  over  the  mixture  draws  out 
the  iron  just  as  if  the  salt  were  not  there.  On  the 
other  hand,  the  salt  can  be  separated  from  the  iron. 
If  the  mixture  is  covered  with  water  and  then  poured 
through  a  filter,  the  particles  of  iron  will  remain  on  the 

paper  in  the  filter.  The 
liquid  which  passes  through 
the  filter  is  known  as  the 
filtrate.  By  boiling  this 
filtrate,  the  water  will 
evaporate,  and  the  salt  will 
remain  in  its  original  form. 
Both  substances  have  been 
recovered  in  their  original 
form  and  no  new  substance 
has  been  formed.  If  two 
or  more  substances  are 
is  placed  together,  and  each 


paper 
the  funnel. 


Fig.     25.       A    filter 
folded  and  placed  in  tl 

beeak"fr'd  T hTmtrltT™"   retains   its   original   prop- 
erties,   the    resulting   sub- 
stance  is  called  a  mechanical  mixture. 

Chemical  compounds.  If  iron  filings  and  powdered 
sulphur  are  thoroughly  ground  together  in  a  mortar, 
a  yellowish  green  substance  results.  As  in  the  case  of 
the  salt  and  the  iron  this  is  again  a  mechanical  mixture, 
from  which  the  sulphur  and  the  iron  can  easily  be 
separated. 


CHEMICAL  PHENOMENA  55 

If  this  mixture  is  placed  in  a  test  tube  and  heated 
in  the  flame  of  a  Bunsen  burner,  a  very  striking  change 
takes  place.  The  mixture  begins  to  glow  at  the  bottom 
of  the  tube,  and  then  the  glow  rapidly  extends  through 
the  entire  mass.  If  the  test  tube  is  now  broken  and 
its  content  examined,  it  will  be  found  to  be  a  brittle 
substance,  which  in  no  way  resembles  the  sulphur  or 
the  iron  with  which  we  started.  The  magnet  will  no 
longer  attract  the  iron,  neither  can  the  sulphur  be 
separated  by  any  physical  process.  A  new  substance 
has  been  formed,  resulting  from  the  action  of  the  heat 
upon  the  mixture  of  iron  and  sulphur.  This  new  sub- 
stance is  iron  sulphide.  Such  a  substance  is  called 
a  chemical  compound.  When  two  or  more  substances 
unite  in  such  a  way  as  to  lose  their  characteristic 
properties,  and  to  form  a  new  substance  with  new 
properties,  such  a  substance  is  called  a  chemical 
compound. 

Elements.  It  has  been  seen  that  iron  sulphide  is 
composed  of  two  entirely  different  substances,  iron 
and  sulphur.  The  question  now  naturally  arises:  do 
these  substances  each  contain  different  substances,  that 
is,  are  they  also  chemical  compounds? 

Chemists  have  tried  in  a  great  many  ways  to  decom- 
pose them,  but  all  their  efforts  have  failed.  Substances 
which  can  not  be  decomposed  into  other  substances  are 
called  elements.  It  is  not  always  possible  to  prove  that 
a  given  substance  is  an  element.  It  is  always  possible 
that  by  some  yet  untried  method  the  supposed  element 


56 


A  YEAR  IN  SCIENCE 


may  be  decomposed  into  other  simpler  forms  of  matter 
and  thus  be  proved  to  be  a  compound.  Water  and 
other  familiar  compounds  were  at  one  time  thought 
to  be  elements. 

An  element  may  be  defined  as  a  substance  Avhich  can 
not  be  separated  into  simpler  substances  by  any  known 
means. 

Number  of  elements.  The  number  of  substances  now 
supposed  to  be  elements  is  not  large.  There  are  eighty- 
four  elements.  Probably  there  are  some  undiscovered, 
but  it  is  generally  believed  that  the  present  number 
will  not  be  greatly  increased.  These  elements  are 
analogous  to  the  letters  of  the  alphabet,  and  by  their 
various  combinations  make  up  the  matter  of  the  uni- 
verse, somewhat  as  letters  form  words. 

About  ten  of  these  elements  are  gases  at  ordinary 
temperatures,  two  are  liquids,  and  all  the  others  are 
solids. 

Each  element  is  designated  by  a  symbol,  which  is  an 
abbreviation  of  the  name,  or  in  some  cases  an  abbrevia- 
tion of  the  Latin  name.  A  list  of  the  more  common 
elements  with  their  svmbols  follows : 


Aluminum 

Antimony 

Argon 

Arsenic 

Bismuth 

Bromine 

Calcium 

Carbon 


Al  Chlorine 

Sb  Copper 

A  Fluorine 

As  Gold 

Bi  Helium 

Br  Hydrogen 

Ca  Iodine 

C  Iron 


Cl  Krypton  Kr 

Cu  Lead  Pb 

F  Magnesium  Mg 

Au  Manganese  Mn 

He  Mercury  Hg 

H  Neon  Ne 

I  Nickel  Ni 

Fe  Nitrogen  N 


CHEMICAL  PHENOMENA 


57 


Oxygen  0  Silicon 

Phosphorus  P  Silver 

Platinum  Pt  Sodium 

Potassium  K  Sulphur 

Radium  Ra  Tin 


Si  Tungsten 

Ag  Uranium 

Na  Xenon 

S  Zinc 
Sn 


W 

U 

Xe 

Zn 


Chemical  synthesis.  We  have  already  learned  that 
if  iron  filings  and  sulphur  are  thoroughly  mixed  and 
then  heated,  a  chemical  compound,  iron  sulphide,  is 
formed.  When  two  or  more  substances  combine  chem- 
ically and  form  a  compound,  the  process  is  known  as 
chemical  synthesis. 

Chemical  Analysis.  Just  as  it  is  possible  for  sub- 
stances to  combine  and  form  more  complex  substances, 
so  also,  it  is  possible  to  decompose  these  complex  sub- 
stances into  the  elements  of  which  they  are  composed. 


Fig.  26.  If  a  glowing  pine  splinter  is  inserted  into  a  test  tube 
containing  highly  heated  mercuric  oxide,  the  splinter  burns  more 
brightly. 


58  A  YEAR  IN  SCIENCE 

A  small  amount  of  mercuric  oxide,  a  light  red  powder, 
is  placed  in  a  test  tube.  The  tube  is  then  thoroughly 
heated.  If,  while  the  tube  is  in  the  flame,  a  glowing  pine 
splinter  is  inserted  into  it,  the  splinter  at  once  breaks 
into  a  flame.  Evidently  there  is  something  being  given  off 
from  the  highly  heated  mercuric  oxide  which  causes  this 
change  in  the  splinter.  This  substance  is  the  gas,  oxygen, 
an  element  which  forms  about  one-fifth  of  the  air. 

If  the  tube  is  allowed  to  cool,  the  inside  of  it  will  be 
found  to  be  covered  with  a  thin  coating  of  mercury. 
Thus  mercuric  oxide  has  been  separated  by  means  of 
heat  into  its  elements,  oxygen  and  mercury.  This 
process  of  separating  or  decomposing  a  compound  into 
its  elements  is  known  as  chemical  analysis. 

Chemical  affinity.  It  is  evident  that  in  the  formation 
of  the  chemical  compound,  iron  sulphide,  the  two 
elements,  iron  and  sulphur,  were  in  some  way  com- 
bined. This  combination  was  brought  about  by  the 
action  of  heat.  The  force  which  caused  these  two 
elements  to  combine  and  which  held  them  together 
when  combined  is  called  chemical  affinity. 

The  attraction,  or  affinity,  which  one  substance  has 
for  another  is  always  the  cause  of  chemical  union. 
Frequently  this  union  does  not  take  place  except 
through  the  action  of  some  agency,  as  heat,  light,  or 
electricity.  \ 

Sometimes  these  same  agencies  may  overcome  this 
attraction  and  as  a  result  cause  the  decomposition  of 
a  compound.  Mercuric  oxide  we  have  learned  is  com- 


CHEMICAL  PHENOMENA  59 

posed  of  mercury  and  oxygen.  It  was  found  possible, 
however,  by  heat  to  overcome  the  attraction  which  the 
mercury  and  oxygen  had  for  each  other  and  thus  to 
decompose  the  compound  -which  they  had  formed  by 
their  union. 


Questions 

1.  Name  two  physical  properties  of  iron. 

2.  Name  one  chemical  property  of  iron. 

3.  Give    an    example    of    a    mechanical    mixture. 
Explain    why    the    example    given    is    a    mechanical 
mixture. 

4.  Is   iron   sulphide    a   mechanical   mixture    or    a 
chemical  compound?     Why? 

5.  Define  the  term  chemical  element. 

6.  How  many  elements  are  there? 

7.  Name  ten  elements.     What  is  the  symbol  for 
each? 

8.  What    are    the    differences    between    chemical 
synthesis  and  chemical  analysis? 

9.  Give    two     examples     of    chemical    synthesis. 
Two  of  chemical  analysis. 

10.  What  is  the  name   given  to  the  force  which 
holds  elements  together  when  they  form  compounds? 

11.  Through    what    agencies    may    this    force    be 
overcome  ? 

12.  State  several  conditions  under  which  elements 
will  unite. 


CHAPTER  IX 
CARBON 

(Carbon  ==  C) 

Introduction.  Carbon,  though  perhaps  not  known 
by  that  name,  in  some  form  is  known  to  all  of  us. 
We  are  all  familiar  with  the  black  soot  which  collects 
on  the  side  of  a  lamp-chimney  from  the  burning  of  an 
unevenly  trimmed  lamp  wick.  To  this  substance  the 
name  lampblack  is  given. 

All  have  seen  the  charred  remains  of  bones  that 
have  been  roasted  out  of  reach  of  air.  This  substance 
we  know  as  bone  black.  Charcoal,  too,  is  somewhat 
familiar  from  its  use  in  filtering  water  or  as  a  deo- 
dorizer, while  coke  and  coal  are  known  as  our  chief 
sources  of  fuel  for  heating  purposes.  The  so-called 
lead  of  the  lead  pencil  is  graphite,  a  form  of  carbon,  while 
the  diamond  is  another  form. 

As  widely  as  these  substances  vary  in  physical 
properties,  yet  each  is  chiefly  carbon.  Carbon  is  the 
most  widely  distributed  of  all  the  known  elements.  It 
is  found  in  all  living  matter,  whether  plant  or  animal, 
and  it  also  forms  a  considerable  part  of  the  earth's 
crust.  In  the  uncombined  or  free  state  it  is  found  as 
diamond,  coal,  and  graphite. 


CARBOK  61 

Charcoal.  If  a  piece  of  charcoal  is  examined  care- 
fully it  will  be  seen  to  look  very  much  like  a  small 
block  of  wood.  And  such,  in  fact,  it  is.  It  is  usually 
made  by  heaping  up  the  small  blocks  of  wood  into 
mounds  and  covering  the  whole  with  soil  and  turf  to 
exclude  the  air.  Then  a  fire  is  started  underneath  the 
wood  and  although  some  of  the  wood  burns,  yet  the 
greater  portion  only  smolders.  The  result  is  that  all 
other  substances  are  driven  off,  leaving  practically 
pure  carbon.  A  more  modern  method  of  producing 
charcoal  is  to  heat  wood  in  closed  iron  ovens.  The 
principle  involved  in  either  case  is  the  same;  namely, 
to  break  down  the  compounds  which  comprise  wood 
into  simpler  substances,  and  drive  off  all  but  carbon. 
Animal  carbon  is  prepared  by  burning  bones  away 
from  air. 

Uses  of  charcoal.  Because  of  its  porous  nature, 
charcoal  is  a  great  absorber  of  gases.  This  quality 
renders  it  of  great  value  in  contributing  to  our  com- 
fort and  welfare.  The  unpleasant  odors  which  arise 
from  sewers  can  be  prevented  by  suspending  bags  of 
charcoal  in  the  man-holes.  Cistern  water  is  kept  sweet 
and  clean  by  filtering  through  charcoal.  In  many 
homes  in  our  cities  all  water  used  for  drinking  and 
cooking  purposes  is  passed  through  charcoal  filters. 
In  passing  through  the  porous  charcoal  the  impurities 
are  removed.  However,  unless  the  filter  is  cleaned 
frequently  it  may  become  a  menace  to  health  rather 
than  a  benefit.  The  pores  in  the  filter  become  clogged 


62  A  YEAR  IN  SCIENCE 

with  impurities  and  furnish  a  hotbed  for  whatever 
germs  may  find  their  way  there.  So,  instead  of  remov- 
ing the  things  that  are  injurious,  it  may  be  the  means 
of  supplying  them.  The  necessity  of  keeping  the  filter 
thoroughly  cleaned  must  be  clear  to  all. 

Charcoal  is  also  used  as  a  decolorizer.  For  this 
purpose,  however,  animal  .charcoal  is  chiefly  used.  If 
you  have  ever  visited  a  sugar  beet  factory,  no  doubt 
you  were  impressed  by  the  difference  of  color  in  the 
dark  sap  from  which  the  sugar  is  made  and  the  beaft- 
tiful  white  crystals  of  commercial  sugar.  This  trans- 
formation in  color  is  brought  about  in  the  large  filters, 
called  charfilters,  which  contain  this  finely  divided 
charcoal  through  which  the  syrup  passes.  Large  quan- 
tities of  charcoal  are  used  in  sugar  refining. 

Lampblack.  Lampblack  or  soot  is  practically  pure 
carbon.  It  is  obtained  by  incomplete  burning;  that  is, 
by  burning  with  a  limited  supply  of  air.  This  can 
be  shown  by  cutting  off  the  air  to  your  Bunsen  flame 
and  holding  a  white  porcelain  plate  over  the  flame. 
The  soot  will  collect  on  the  plate.  This  finely  divided 
black  powder  furnishes  the  pigment  for  the  manufac- 
ture of  printer's  ink  and  paint. 

Coal.  Generally  speaking,  coal  is  divided  into  soft, 
or  bituminous,  and  hard,  or  anthracite  coal.  The  dif- 
ference is  greater  than  the  mere  physical  difference  of 
degrees  of  hardness  and  is  explained  by  the  greater 
percentage  of  carbon  found  in  the  hard  coal.  Anthra- 


CARBOX 


63 


cite  coal  generally  consists  of  about  95%  carbon  while 
bituminous  coal  contains  80%  or  less  of  carbon. 


Copyright  by  Underwood  d-  Underwood,  N.  Y. 
Fig.  27.     Mining  anthracite  coal  three  miles  underground. 

Coal  is  wood  that  has  undergone  great  changes  dur- 
ing past  centuries.  The  harder  the  coal  the  longer 
this  change  has  been  taking  place.  During  a  period 
of  the  earth's  history  known  as  the  Carboniferous 
Age,  the  earth  was  covered  with  a  luxurious  growth 


64 


A  YEAR  IX  .SCIENCE 


of  vegetation  under  swamp  and  marsh  conditions.  As 
this  fell  and  accumulated  year  after  year,  and  century 
after  century,  and  became  submerged,  many  of  the 
more  volatile  gases  were  driven  off,  with  some  of  the 
carbon,  no  doubt,  but  much  of  the  carbon  was  pre- 
served. As  the  pressure  of  the  accumulating  Aveight 
increased,  further  changes  took  place  until  eventually 
coal,  our  chief  source  of  heating  fuel,  was  produced. 


Copyright  by  Underwood  tC-  Undenvood,  N.  Y. 

Fig.   28.     Cutting  peat  in  Ireland,  where  it  is  used  as  a  substitute 

for  coal. 

Successive  stages  in  coal  formation  are  wood,  peat, 
lignite  or  brown  coal,  soft  or  bituminous  coal,  and  hard 
or  anthracite  coal. 

Coke  is  produced  from  coal  in  very  much  the  same 
manner  that  charcoal  is  produced  from  Avood.  When 


CARBON  65 

coal  is  heated  away  from  air,  coke  is  the  solid  sub- 
stance that  remains. 

The  chief  use  of  coke  is  for  fuel  for  coke  ovens, 
blast  furnaces,  and  steam  engines.  It  is  superior  to 
soft  coal,  because  it  gives  off  more  heat;  but  inferior 
to  hard  coal,  because  it  burns  more  rapidly  and 
requires  more  attention.  Because  it  is  a  good  con- 
ductor of  electricity  it  is  used  also  in  the  electrical 
industry. 

Graphite.  Graphite  is  another  form  of  carbon  taken 
from  mines  in  the  earth.  The  best  of  these  are  found 
in  Siberia  and  Ceylon,  though  much  is  mined  in  Eng- 
land, California,  and  New  York.  Graphite  differs  from 
other  forms  of  carbon  in  that  it  is  very  soft.  Its  uses 
are  many :  as  a  lubricant  for  machines,  as  polish  for 
stoves,  as  a  covering  to  conduct  the  electric  current 
in  electrotyping,  and  mixed  with  clay,  to  supply  the 
"lead"  of  the  lead  pencil. 

In  the  manufacture  of  lead  pencils,  graphite  is  mixed 
with  clay,  and  worked  up  into  a  pasty  mass.  From 
this  pasty  mass  the  thin  rods  of  the  pencil  are  produced 
which  are  finally  encased  in  the  wood.  The  hardness 
of  the  pencil  depends  upon  the  relative  proportions 
of  graphite  and  clay;  the  more  clay  the  harder  the 
pencil. 

Diamond.  The  diamond  is  pure  carbon.  It  differs 
from  other  forms  of  carbon  in  its  hardness,  being  the 
hardest  substance  known  in  nature.  Because  of  its 
rarity  it  is  a  very  costly  gem,  its  value  being  deter- 


66  A  YEAK  IN  SCIENCE 

mined  by  the  clearness  of  its  crystals  which  refract 
the  light  in  passing  through  it  into  brilliant  colors. 
The  refractive  power  of  the  diamond  is  increased  by 
cutting  its  surface  into  numerous  facets.  Being  the 
hardest  substance  known,  it  takes  diamond  to  cut  dia- 
mond, so  this  process  is  accomplished  by  grinding  tho 
stone  to  be  cut  with  black  and  imperfect  pieces  of 
diamond  which  are  valueless  as  gems. 

Diamonds  which  are  valueless  as  jewels  are  of  much 
value  in  pointing  glass  cutters  and  in  making  drills 
to  drill  rocks. 

The  most  valuable  diamond  mines  are  the  Kimberly 
mines  of  South  Africa,  though  the  stone  is  found  in 
smaller  deposits  in  South  America  and  Australia. 

Carbon  dioxide  =  C02.  Burning  is  a  phenomenon 
familiar  to  all  and  yet  in  the  process  many  chemical 
changes  may  be  taking  place.  The  visible  results  are 
that  the  object  burned  is  separated  into  smoke,  flame, 
and  ash,  together  with  the  heat  given  off.  Another 
product  of  most  burning  is  an  invisible  gas  called 
carbon  dioxide.  This  gas  is  formed  by  the  union  of 
the  oxygen  of  the  air  with  the  carbon  in  the  substance. 
It  may  be  expressed  as  C  +  2  X  0  =  C02  in  which  two 
parts  of  oxygen  combine  with  one  part  of  carbon  to 
form  carbon  dioxide.  It  is  constantly  emitted  wherever 
there  are  living  organisms,  for  all  living  forms  "burn" 
carbon  in  the  body,  and  the  carbon  dioxide  is  given  off 
in  breathing.  Even  in  decay,  plant  and  animal  forms 
give  off  this  gas. 


CARBOX  67 

Preparation  and  test  for  carbon  dioxide.  Carbon 
dioxide  may  be  supplied  in  many  ways,  but  the  sim- 
plest method  for  class  use  is  to  place  a  few  pieces  of 


Fig-.  29.  The  action  of  the  hydrochloric  acid  on  the  pieces  of 
marble  in  the  test  tube  decomposes  them,  releasing  carbon  dioxide. 
The  gas  escapes  through  the  bent  tube  into  the  bottle. 

marble  in  a  test  tube,  and  pour  hydrochloric  acid  on  it. 
In  the  chemical  action  which  takes  place  between  the 
marble  and  the  hydrochloric  acid,  carbon  dioxide  is 
given  off  and  a  salt  (calcium  chloride)  and  water  are 
left  in  the  tube. 

If  a  bottle  of  this  gas  is  collected  it  will  be  found 
to  be  colorless,  with  little  taste  or  odor.  It  is  about 
Il/2  times  as  heavy  as  air  and  thus  can  be  collected 


68  A  YEAR  IN  SCIENCE 

with  the  bottle  upright;  for,  as  the  heavier  gas  enters, 
the  air  is  forced  out.  If  a  burning  pine  splinter  is 
inserted  into  a  bottle  of  carbon  dioxide  it  will  be 
extinguished  immediately.  It  neither  burns  nor  sup- 
ports combustion.  If  lime  water  is  poured  into  a  bottle 
containing  carbon  dioxide,  and  shaken,  it  at  once  turns 
a  milky  color.  This  is  the  test  for  carbon  dioxide  and 
is  universally  used. 

Balance  of  carbon  dioxide  maintained.  From  the 
great  supply  of  carbon  dioxide  constantly  pouring  into 
the  air  it  would  seem  that  life  on  earth  would  soon  be 
endangered.  However,  carbon  dioxide  has  its  place 
in  nature  as  it  provides  some  of  the  food  for  green 
plants.  In  the  process  of  food-making,  green  plants 
take  the  carbon  dioxide  from  the  air  and  water  from 
the  soil,  and  in  the  presence  of  sunlight  convert  them 
into  starch  (or  food  for  the  plant).  Oxygen  is  given 
back  to  the  air  by  the  plant  as  a  waste  product  from 
this  process.  Thus  the  proper  balance  of  carbon 
dioxide  in  the  air  is  maintained. 

Commercial  uses  of  carbon  dioxide.  Carbon  dioxide 
is  soluble  in  water,  which  at  ordinary  temperature 
absorbs  an  amount  about  equal  to  its  own  volume. 
Under  pressure,  however,  it  may  be  charged  with  many 
times  its  own  volume.  This  may  be  observed  at  any 
ordinary  soda  fountain.  Soda  water  is  made  by  simply 
charging  water  with  carbon  dioxide  under  pressure. 
It  is  then  kept  in  sealed  jars  away  from  the  air.  When 
soda  is  drawn  at  the  fountain,  the  effervescence  is 


CARBON 


69 


due    to    the    rushing    forth    of    the    confined    carbon 
dioxide. 

If  carbon  dioxide  is  poured  over  a  burning  candle, 
the  flame  is  extinguished  at  once.  Carbon  dioxide, 
being  heavier  than  the  air,  forms  a  blanket  or  cover- 
ing about  the  candle  thereby  excluding  the  air  or  oxy- 
gen, and  without  oxygen  fire  is  impossible. 

This  fact  gave  rise  to  carbon  dioxide  fire  extin- 
guishers. These  are  made  of  certain  chemicals,  which 
when  placed  together  produce 
carbon  dioxide.  The  chemicals 
commonly  used  are  bicarbonate 
of  soda  and  sulphuric  acid.  The 
extinguisher  consists  of  a  metal- 
lic case  containing  a  small  vessel 
of  strong  sulphuric  acid  em- 
bedded in  the  bicarbonate  of 
soda.  When  the  extinguisher  is 
inverted  the  acid  mixes  with  the 
soda,  producing  carbon  dioxide 
which  escapes  through  a  tube. 
As  this  gas  is  poured  upon  a 
burning  object,  it  forms  a  layer 
of  the  heavier  gas  about  the 
object,  excluding  the  oxygen 
and  thus  extinguishing  the 
fire. 


Fig.  30.    Inside  view 
of  a  fire  extinguisher. 


Carbon  dioxide  also  plays  an  important  part  in  a 
process  which  is  familiar  to  all  of  us,  the  rising  of 


70  A  YEAR  IN  SCIENCE 

dough  in  bread  making.  As  a  result  of  the  action  of 
yeast,  the  sugar  in.  bread  is  broken  down  into  carbon 
dioxide  and  small  quantities  of  alcohol.  The  firm 
dough  then  swells  because  the  gas  imprisoned  within 
it  forms  air  spaces.  In  baking  the  dough,  the  spaces 
are  enlarged  as  the  gas  escapes,  and  at  the  same  time 
the  alcohol  is  evaporated. 

Yeast  is  not  always  used  to  produce  this  carbon 
dioxide.  Sometimes,  as  in  soda  biscuits,  baking  soda 
(bicarbonate  of  soda)  is  used  and  to  it  is  added  cream 
of  tartar  or  sour  milk.  In  either  case,  by  the  action 
of  the  cream  of  tartar  or  the  sour  milk  upon  the  soda, 
carbon  dioxide  is  given  off.  If  baking  powder  is  used, 
as  in  baking  powder  biscuits,  cakes,  and  many  other 
foods,  the  action  of  the  substances  within  the  baking 
powder  is  such  as  to  liberate  carbon  dioxide.  This 
escapes  through  the  dough  and  makes  it  light  and 
porous. 

Questions 

1.  Chemically  speaking,  what  is  charcoal? 

2.  How  is  charcoal  made? 

3.  To  what  various  uses  is  it  put? 

4.  How  is  lampblack  produced? 

5.  Has  lampblack  a  commercial  value  ?  What  is  it  ? 

6.  What  is  coal? 

7.  What  are  the  successive  stages  in  its  formation  ? 

8.  Look  up  all  the  material  you  can  on  coal  forma- 
tion and  write  an  essay  on  it. 

9.  How  is  coke  made  from  coal? 


CARBON  71 

10.  For  what  purposes  is  coke  used? 

11.  Where  are  the  best  graphite  mines? 

12.  What  are  the  uses  of  graphite? 

13.  How  are  lead  pencils  made  ? 

14.  Diamond    and    coal    are    both    carbon.      What 
causes  the  great  difference  in  the  market  values  of  these 
two  substances?    Three  reasons. 

15.  Where  are  the  best  diamond  mines  located? 

16.  Do  you  know  how  diamonds  are  mined?    Look 
it  up  and  bring  this  information  to  class  with  you. 

17.  How  is  carbon  dioxide  produced? 

18.  Is  it  necessary  to  life? 

19.  Is  it  poisonous? 

20.  Would  too  much  of  it  prove  fatal  to  life  ?    Why  ? 

21.  Explain  fully  why  people  and  other  animals  are 
sometimes   killed  in   going  down  into   old  wells   and 
mines. 

22.  What  is  the  test  for  the  presence  of  carbon 
dioxide  ? 

23.  Is  there  any  soda  in  ' '  soda  water ' '  ? 

24.  Whence  then  does  it  receive  its  name? 

25.  What  causes  the  effervescence  of  "soda  water"? 


CHAPTER  X 

PHOSPHORUS 

(Phosphorus  =  P) 

Introduction.  Phosphorus  is  not  found  in  the  free 
state  in  nature,  but  in  compounds,  in  small  quantities 
rather  widely  distributed.  It  is  a  part  of  all  living- 
matter  and  is  found  in  all  fertile  soils,  as  plants  can 
not  grow  without  phosphorus.  Large  deposits  of  'min- 
erals are  found  containing  phosphates,  which  are 
extensively  mined  for  use  as  fertilizers.  Bone  consists 
of  80%  of  calcium  phosphate,  which,  together  with  the 
phosphates  found  in  large  mineral  deposits,  form  the 
chief  sources  of  commercial  phosphorus. 

Preparation.  In  obtaining  phosphorus  from  bones 
the  combustible  matter  is  burned  out,  leaving  bone-ash 
behind. 

Bone-ash  or  a  pure  mineral  phosphate  is  then  heated 
with  sand  and  carbon  in  an  electric  furnace.  In  the 
heating,  phosphorus  vapor  escapes  through  tubes  and 
is  led  under  water  where  it  condenses  in  molds. 

Properties.  Yellow  phosphorus  in  the  pure  state  is 
a  translucent,  waxy  solid  which  when  exposed  to  light 
takes  on  a  coating  of  darker  color.  If  a  piece  of  yelloAv 
phosphorus  is  exposed  to  the  air,  it  will  begin  to  give 

72 


PHOSPHORUS 


73 


off  white  fumes  almost  immediately  and  if  left  thus 
exposed  for  a  minute  or  two,  will  ignite.  Because 
it  ignites  at  such  a  low  temperature,  phosphorus  must 

H 


M 


Fig-.  31.  Phosphorus  furnace.  A  mixture  of  calcium  phosphate, 
sand,  and  carbon  is  admitted  at  H  through  T.  T  is  then  closed  and 
T'  opened.  The  mixture  is  slowly  admitted  over  the  screw  S  and 
drops  between  electrodes  A  and  C.  The  slag  which  forms  flows  out 
at  M.  Phosphorus  vapor  and  carbon  dioxide  pass,  out  through  R. 
The  phosphorus  condenses  in  the  water  W,  and  the  carbon  dioxide 
bubbles  up  and  passes  off  through  the  water. 

always  be  kept  under  water.  It  must  always  be  cut 
under  water,  for  the  friction  of  the  knife  caused  in  the 
cutting  will  raise  its  temperature  to  the  point  of  burn- 
ing. Great  care  must  be  exercised  in  dealing  with 
phosphorus  and  forceps  should  be  used  to  handle  it. 
If  touched  by  the  hands  the  heat  of  the  body  may 
ignite  it  and  cause  a  burn.  A  phosphorus  burn  is  very 
serious,  the  wound  requiring  months  to  heal.  Phos- 
phorus is  very  poisonous,  and  great  care  must  be  taken 


74  A  YEAR  IN  SCIENCE 

not  to  breathe  the  fumes.  Because  of  the  rapidity,  with 
which  oxygen  and  phosphorus  unite,  phosphorus  emits 
a  light  when  exposed  to  air.  This  property  is  known 
as  phosphorescence.  If  yellow  phosphorus  is  heated  in 
closed  vessels  to  a  temperature  of  250°C.  to  300°C., 
its  nature  changes  completely,  producing  the  form 
called  red  phosphorus.  On  further  heating  it  under- 
goes another  change  and  becomes  yellow  phosphorus  once 
more. 

Red  phosphorus  is  a  dull  red,  powdery  substance, 
very  inactive  and  perfectly  safe  to  handle.  It  does  not 
give  off  a  light  as  does  the  yellow  phosphorus,  neither 
is  it  poisonous. 

Uses  of  phosphorus.  Because  of  its  poisonous  nature 
yellow  phosphorus  is  used  in  preparing  poison  for  rats, 
mice,  and  other  vermin.  Its  chief  use,  however,  as  well 
as  that  of  the  red  phosphorus,  is  in  the  manufacture  of 
matches. 

Friction  match.  In  preparing  the  common  friction 
match,  the  end  of  the  stick  is  soaked  in  a  mixture 
usually  containing  paraffin,  sulphur,  phosphorus,  glue, 
and  some  compound  containing  a  great  deal  of  oxygen. 
On  striking  the  match  the  heat  produced  from  the  fric- 
tion kindles  the  phosphorus,  which  unites  with  the 
oxygen  in  the  compound  on  the  head  of  the  match,  and 
also  with  the  oxygen  in  the  air.  The  sulphur  and 
paraffin  are  then  ignited,  and  their  burning  sets  fire 
to  the  wood. 

Safety  match.     The  safety  match  differs  from  the 


PHOSPHORUS  75 

friction  match  in  that  the  phosphorus,  instead  of  being 
placed  on  the  head  of  the  match,  is  placed  on  the  side 
of  the  box.  For  this  purpose  red  phosphorus  is  used. 
To  ignite  the  match  it  is  necessary  to  strike  its  head 
on  the  side  of  the  box  or  some  similar  surface.  The 
heat  thus  produced  is  sufficient  to  convert  a  small 
portion  of  the  red  phosphorus  on  the  box  to  yellow 
phosphorus,  which  kindles  and  ignites  the  substances 
on  the  head  of  the  match. 

Dangers  of  friction  match.  When  we  consider  the 
ease  with .  which  ordinary  friction  matches  ignite,  the 
danger  resulting  from  leaving  them  about  becomes 
apparent.  Disastrous  fires  with  thousands  of  dollars 
loss,  have  resulted  from  mice  or  rats  clawing  matches ; 
from  children  striking  them,  or  from  their  being 
stepped  on.  Because  of  the  fact  that  the  safety  match 
will  not  easily  ignite  unless  rubbed  on  the  specially 
prepared  surface,  it  is  far  safer.  The  chance  of  acci- 
dentally igniting  them  is  much  less,  and  in  some  coun- 
tries, notably  Switzerland,  manufacture  of  the  common 
friction  match  with  yellow  phosphorus  is  forbidden. 
Property  destruction  is  not  the  only  loss  resulting 
from  the  manufacture  of  the  friction  match.  The 
continued  breathing  of  the  vapor  from  the  phosphorus 
by  men  in  the  factories  produces  an  incurable  disease 
called  necrosis.  This  is  characterized  by  falling  out 
of  the  teeth,  and  the  ulceration  and  decay  of  the  jaw 
bones.  The  only  way  to  prevent  the  spread  of  the 
disease  is  to  remove  the  affected  part.  Because  of  the 


76  A  YEAR  IN  SCIENCE 

dangers  of  poisoning  resulting  from  the  common  friction 
match,  its  manufacture  should  be  forbidden. 


Questions 

1.  What  is  the  chief  source  of  phosphorus? 

2.  How  is  it  prepared? 

3.  What  are  the  two  different  kinds  of  phosphorus? 

4.  What  are  some   of  the  more  prominent  char- 
acteristics of  each? 

5.  Why  should  yellow  phosphorus  be  kept  under 
water?     Why  should   it  never  be   touched   with   the 
hands? 

6.  What  are  the  chief  uses  of  phosphorus? 

7.  Write  an  essay  on  the  match  industry. 

8.  Why  do  some  countries  forbid  the  manufacture 
of  friction  matches? 


CHAPTER  XI 

SULPHUR 

(Sulphur  =  S) 

The  sulphur  ordinarily  used  in  the  laboratory  is  of 
two  kinds,  roll  sulphur  and  flowers  of  sulphur.  The 
difference  is  merely  a  physical  one  and-  is  due  to  the 
method  by  which  each  is  prepared  from  the  element 
as  it  is  found  in  nature. 

Occurrence.  Sulphur  is  found  both  in  the  free  state 
and  in  combination  with  other  elements,  though  com- 
mercial sulphur  is  prepared  chiefly  from  sulphur  in 
the  free  state.  It  is  found  very  widely  distributed, 
being  usually  associated  with  volcanic  regions.  The 
largest  deposits  occur  in  Sicily,  Texas,  and  Louisiana, 
with  Japan,  Mexico,  and  California  adding  to  the 
world's  supply.  In  Yellowstone  Park  it  is  found  in 
sulphur  springs.  It  is  also  found  in  many  vegetables 
and  in  the  yolk  of  eggs,  and  it  forms  no  inconsiderable 
part  of  the  human  body,  more  than  four  ounces  of  it 
being  present  in  the  body  of  a  man  of  ordinary 
size.  Sicily  formerly  held  first  rank  in  the  amount 
of  sulphur  annually  given  to  the  markets  of  our  coun- 
try. This  was  due  to  the  great  abundance  of  the 
element  throughout  that  region  and  to  the  cheapness 

77 


78 


A  YEAR  IN  SCIENCE 


Fig.  31 


Copyright  by  Underwood  &  Underwood,  N.  Y. 
A  volcano  sending  forth  steam  and  sulphurous  fumes. 


of  labor  there.  Today  Louisiana  has  outstripped  Sicily 
because  of  the  discovery  of  new  methods  of  working. 
Preparation.  Although  found  deposited  in  immense 
beds  in  the  free  state,  sulphur  is  practically  always 
mixed  with  various  kinds  of  earthy  substances.  Before 


SULPHUR  79 

the  element  can  be  of  commercial  value,  it  is  necessary 
to  free  it  of  all  impurities.  In  Sicily  where  the  largest 
deposits  occur,  this  is  done  by  digging  out  the  sulphur 
and  heaping  it  into  large  piles.  The  mounds  are  then 
covered  with  sod  and  dirt  and  a  fire  is  started  under- 
neath. 

The  heat  produced  causes  the  sulphur  to  melt,  and 
it  is  then  run  out  into  troughs.  Naturally  much  of 
the  sulphur  is  burned  and  passes  off  as  sulphur  dioxide. 
Thus  a  large  percentage  of  waste  results.  This  loss 
has  now  been  overcome  by  heating  the  substances  out 
of  contact  with  the  air. 

The  method  is  first  to  place  the  ore  in  heaps  in 
closed  vessels  and  to  heat  it  until  the  sulphur  melts  and 
thus  separates  from  the  earthy  substances.  The  low 
melting  point  of  sulphur  makes  this  possible.  It  is 
then  further  purified  by  heating  it  in  closed  iron  ves- 
sels having  ducts  leading  into  a  cooling  chamber  made 
of  bricks.  The  sulphur  vaporizes;  when  the  vapor 
conies  into  the  cooling  chamber  it  is  suddenly  cooled, 
and  some  of  it  collects  as  fine  powder  on  the  Avails  of 
the  chamber.  This  form  is  known  as  flowers  of  sul- 
phur. Most  of  the  sulphur  vapor  condenses  to  the 
liquid  form  and  falls  to  the  bottom  of  the  cooling 
chamber.  It  is  then  run  into  molds  where  it  hardens 
into  the  cylindrical  shaped  rods  known  as  roll  sulphur. 
The  method  used  in  the  United  States  consists  in 
sinking  into  the  sulphur  beds  four  concentric  iron 
tubes.  The  inner  tube  is  one  inch  in  diameter;  the 


80 


A  YEAR  IN  SCIENCE 


next,  three;  the  third,  six;  and  the  outer  tube,  ten. 
"Water  heated  under  pressure  much  above  the  boiling 
point  is  forced  through  the  three  inch  tube  into  the 


Permission  United  States  Geological  Survey. 

Fig.    33.      Sulphur   which   has   been   brought   to    the   surface   and 
consolidated,  ready  for  shipment,  at  Sulphur,  Louisiana. 


beds  to  melt  the  sulphur.  Air  under  pressure  is  forced 
through  the  one  inch  tube.  The  melted  sulphur  mixed 
with  air  then  bubbles  up  through  the  outer  tubes.  The 
sulphur  is  collected  in  large  bins  built  of  wood,  where 
it  solidifies  to  form  large  blocks  of  practically  pure 
sulphur.  These  blocks,  often  containing  as  much  as 
100,000  tons,  are  broken  up  by  blasting  and  prepared 
for  market. 

Physical  properties.    Sulphur  is  pale  yellow  in  color, 
and  without  taste  or  odor.     It  is  insoluble  in  water. 


SULPHUR 


81 


When  heated  to  114.5°  C.,  sulphur  melts  to  a  clear, 
amber  colored  liquid  which  flows  almost  as  readily  as 
Avater.  As  the  temperature  is  increased,  the  color  of 
the  liquid  gradually  thickens  and  passes  through  the 
various  shades  of  amber  to  a  dark  red  wine  color,  until 
at  200° C.  the  color  is  almost  black  and  the  mass  so 
thick  and  viscous  that  the  vessel  in  which  it  is  heated 


Figr.    34. 


Melted    sulphur    forms    an    elastic    mass    when    suddenly 
cooled  in  water. 


may  be  inverted  without  the  mass  running  out.  Fur- 
ther heating  converts  it  into  a  black  liquid  again, 
which  if  suddenly  cooled  by  pouring  into  water,  will 
be  found  to  be  elastic  in  nature.  If  the  temperature 
is  increased  to  448 °C.,  the  liquid  boils,  giving  off  a 


g2  A  YEAR  IN  SCIENCE 

pale  yellowish  gas,  which  if  collected  on  a  cool  surface 
will  be  found  to  be  the  yellow  sulphur  with  which  we 
started.  On  cooling,  the  same  changes  take  place  in 
reverse  order. 

This  entire  cycle  of  changes  through  which  sulphur 
has  passed  is  purely  physical  and  due  to  the  different 
degrees  of  temperature  to  which  it  was  subjected. 

Chemical  properties.  Sulphur  burns  in  the  air  or  in 
oxygen  with  a  pale  blue  flame,  forming  an  oxide  of 
sulphur  (sulphur  dioxide).  It  unites  very  readily  with 
most  metals,  when  heated,  to  form  a  compound.  This 
is  shown  by  heating  a  little  sulphur  on  a  piece  of 
silver.  The  black  deposit  formed  is  a  compound  from 
the  union  of  the  sulphur  and  silver  and  is  called  sul- 
phide of  silver. 

Uses.  The  uses  of  sulphur  are  many.  We  have 
already  mentioned  its  use  in  the  manufacture  of 
matches.  Sulphur  is  one  of  the  ingredients  found  in 
the  head  of  the  match.  Its  kindling  point  is  above  that 
of  phosphorus,  which  produces  the  spark  when  lighted, 
and  below  that  of  wood.  So  the  sulphur  ignites  from 
the  phosphorus  and  its  burning  ignites  the  wood. 

Sulphur  dioxide,  the  gas  produced  when  sulphur 
burns,  has  a  very  suffocating  odor.  It  is  impossible 
for  germ  life  to  exist  long  in  its  presence ;  therefore  it 
is  a  valuable  disinfecting  agent.  It  is  very  commonly 
used  in  fumigating  rooms  that  have  been  occupied  by 
persons  having  contagious  diseases.  This  is  done  by 
making  the  room  as  nearly  air  tight  as  possible,  then 


SULPHUR  83 

the  gas  is  formed  by  burning  sulphur  in  the  room. 
A  safer  method,  however,  is  to  purchase  a  small  can 
of  sulphur  dioxide  in  liquid  form.  On  opening  the  can 
the  gas  escapes  into  the  room. 

Sulphur  dioxide  is  also  used  for  bleaching  purposes, 
especially  for  straw,  feathers,  and  fabrics. 

The  elastic  nature  of  the  suddenly  cooled  sulphur 
gives  a  hint  of  another  commercial  use  of  sulphur. 
Much  of  it  is  used  in  vulcanizing  rubber. 

It  is  also  used  in  making  fireworks,  gunpowder,  and 
as  a  spray  to  free  trees,  shrubs,  and  vineyards  from 
attacking  fungi. 

Questions 

1.  Name   the   different   kinds   of   sulphur   in   the 
laboratory. 

2.  How  do  they  differ? 

3.  Is  this  a  chemical  or  a  physical  difference? 

4.  Where  is  sulphur  found? 

5.  How  is  it  mined  in  Sicily  ? 

6.  How  in  Louisiana? 

7.  What  are  the  chief  physical  characteristics  of 
sulphur  ? 

8.  What  are  some  of  its  chemical  characteristics? 

9.  Name  a  number  of  commercial  uses  of  sulphur. 

10.  What  part  does  sulphur  play  in  the  manufac- 
ture of  the  friction  match? 

11.  How  is  sulphur  dioxide  produced?     What  are 
some  of  its  uses? 


CHAPTER  XII 

IRON 

(Iron  =  Fe) 

Introduction.  Of  all  the  metals,  iron  is  by  far  the 
most  useful  to  the  human  race. 

Railroads  cover  the  surface  of  the  earth  with  a  net- 
work of  iron  rails  over  which  iron  engines  draw  iron 
cars.  The  automobile,  the  bicycle,  the  buggy,  the  ocean 


Fig-.  35.     Steel  is  used  extensively  in  modern  building. 

liner,  and  the  aeroplane,  all  contain  more  or  less  iron 
in  their  construction.  Even  in  riding  horseback  one  is 
unable  to  escape  the  accompaniment  of  iron,  for  the 
horse  is  shod  with  iron  shoes  and  the  bridle  and  saddle 

84 


IRON  85 

contain  a  liberal  amount.  Practically  all  construction 
is  fundamentally  of  iron  which  has  been  built  with 
iron  tools. 

Thus  iron  has  become  an  absolute  necessity  to  the 
physical  wants  of  the  race.  Its  great  utility  is  due  to 
the  fact  that  it  can  be  made  into  so  many  different 
things. 

Occurrence.  Iron  is  not  found  in  nature  in  the  state 
in  which  we  know  it  commercially,  though  occasionally 
free  iron  which  has  dropped  to  the  earth  from  meteors 
is  found.  It  is  widely  distributed  over  the  whole  earth 
combined  with  other  substances,  in  which  form  it  is 
known  as  iron  ore.  It  exists  chiefly  in  combination 
with  oxygen,  carbon,  or  sulphur  in  the  form  of  oxides, 
carbonates,  or  sulphides.  The  United  States  is  the 
greatest  iron  producing  country  in  the  world.  The 
iron  mines  of  the  Lake  Superior  region  are  the  richest 
and  best  known,  and  supply  a  large  part  of  the  world's 
annual  output. 

The  south  also  contains  rich  mines,  Birmingham,  Ala- 
bama, being  the  center  of  the  industry  in  the  south. 
This  is  due  to  the  fact  that  coal  and  limestone,  two 
other  substances  necessary  in  iron  making,  are  found 
deposited  there.  The  mineral  kingdom  is  not  the  only 
place  where  iron  is  found.  The  element  is  necessary  for 
the  life  of  all  green  plants  and  is  found  in  the  hemoglobin 
of  the  blood,  where  it  plays  a  very  important  function 
in  carrying  oxygen  to  the  various  parts  of  the  body. 

Preparation  from  ore.     To  produce  the  metal  iron 


86 


A  YEAR  IN  SCIENCE 


from  the  various  substances  with  which  it  is  combined 
in  the  ore,  it  is  necessary  to  separate  the  element  from 
them. 

This  is  accomplished  by  heating  a  mixture  of  the  ore, 
coal  or  coke,  and  limestone  in  a  blast  furnace.  The 
blast  furnace  is  from  50  to  100  feet  high  with  a  diam- 
eter varying  from  fifteen  to  twenty  feet.  It  is  lined 
on  the  inside  with  firebricks.  A  furnace  with  a  body 


Courtesy  of  American  Steel  tt-  Wire  Co. 
.    oduces  pig  iron.     One  furm 
with  the  four  stoves  which  heat  the  blast. 


Fig.  36.     A  blast  furnace  produces  pig  iron.     One  furnace  is  shown 

•rhi  " 


of  these  dimensions  will  use  a  great  deal  of  fuel  and 
for  its  combustion  much  air  is  necessary.  This  air  is 
supplied  through  pipes  from  the  bottom  under  very 
great  pressure.  Thus  the  gases  in  the  ore  are  burned 


IRON 


87 


out,  the  lime  combines  with  the  clay-like  impurities  of 
the  ore  to  form  a  slag,  and  the  molten  iron  sinks  to 
the  bottom  of  the  furnace  where  it  is  drawn  off  through 
holes  into  molds.  These  molds  are  called  ' '  pigs, ' '  from 
which  the  iron  gets  its  name  of  pig  iron. 


Courtesy  of  American  Steel  <C-  Wire  Co. 

Fig.  37.  Bessemer  converters  In  which  pig  iron  is  made  into 
steel.  The  view  on  the  right  shows  the  inside  of  a  converter  ;  the 
middle  one  shows  a  converter  in  action  throwing  sparks  of  burning 
steel  particles  into  the  air.  The  converter  on  the  left  is  discharging 
the  finished  steel. 


Three  forms  of  iron.  The  three  forms  of  iron  known 
to  commerce  are  cast  iron,  wrought  iron,  and  steel. 
Each  kind  is  truly  iron,  though  having  very  widely 
differing  physical  properties.  Pure  iron  is  practically 
unknown.  The  different  kinds  contain  carbon  and 
small  amounts  of  other  substances  in  composition. 


88  A  YEAR  IN  SCIENCE 

Cast  iron  contains  the  largest  amount  of  carbon, 
varying  from  2  to  5%.  It  is  a  brittle  substance  and 
can  be  used  only  where  it  is  not  to  be  subjected  to 
great  shocks.  It  is  used  in  casting  articles  such  as 
stoves,  radiators,  machines,  etc. 


Courtesy  of  American  Steel  d  Wire  Co. 

Fig.  38.     Ore  of  less  purity  than  that  used  in  the  Bessemer  process 
is  made  into  fine  steel  by  the  open  hearth  process. 

Wrought  iron  is  the  purest  form  of  iron,  containing 
less  than  1%  of  impurities  and  usually  less  than  0.2% 
of  carbon.  It  is  made  from  cast  iron  by  burning  out 
the  carbon.  It  is  a  tough  iron  which  can  be  bent, 
stretched,  hammered,  or  rolled  into  various  forms.  It 
is  easily  forged  and  welded  and  thus  becomes  the  iron 
of  greatest  use  to  the  blacksmith. 

Steel  is  also  produced  from  cast  iron  by  burning  out 


IRON  89 

the  carbon.  It  contains  less  carbon  than  cast  iron  and 
slightly  more  than  wrought  iron.  Its  carbon  content 
varies  from  practically  nothing  in  some  forms  to  a, 
little  less  than  2%  in  others.  Steel  serves  many  uses 
for  mankind,  from  the  steel  rail  to  the  main  spring  of 
a  watch. 

Questions 

1.  Following  are  some  of  the  properties  of  iron. 
Classify  them  under  the  head  of  physical  or  chemical 
properties:      (a)    it   rusts   easily,    (b)    melts   at   1,200 
degrees  C.,  (c)  has  a  specific  heat  of  0.114,  (d)  burns 
in  oxygen,   (e)   is  magnetic,  (f)  has  a  density  of  7.8, 
(g)  "dissolves"  in  hydrochloric  acid.    How  would  you 
prove  your  answer  for  (g)  ? 

2.  Name  a  number  of  commercial  uses  of  iron. 

3.  How  is  it  found  in  nature? 

4.  Look  up  material  on  how  commercial  iron  is 
made  from  the  ore  and  write  an  essay  on  it  for  class. 

5.  Name  the  three  different  kinds  of  iron  enumer- 
ated in  the  text. 

6.  How  do  they  differ  from  each  other? 

7.  To  what  uses  is  each  different  kind  put? 


CHAPTER  XIII 

OXYGEN 

(Oxygen  —  0) 

Introduction.  Oxygen  is  by  far  the  most  abundant 
of  all  the  elements.  It  is  found  practically  everywhere, 
either  in  the  free  state  or  in  combination  with  other 
elements.  It  is  found  in  the  air  in  the  free  state  and 
forms  one-fifth  of  its  volume.  In  combination  with 
another  element,  hydrogen,  it  forms  eight-ninths  of 
the  weight  of  water. 

Nearly  one-half  of  the  earth's  crust  is  oxygen  in 
combination  with  other  elements.  Even  living  matter 
is  made  up  largely  of  oxygen  in  combination  with  other 
substances.  The  human  body  contains  66%  oxygen. 

Oxygen  is  also  one  of  the  most  important  of  the 
elements.  If  a  lighted  candle  is  placed  in  a  glass  jar 
and  the  jar  tightly  closed,  the  flame  will  soon  be  extin- 
guished. Then  if  the  gas  in  the  jar  is  examined  no 
oxygen  will  be  found.  Likewise,  if  a  living  being  is 
enclosed  with  a  limited  supply  of  oxygen,  as  some- 
times occurs  in  the  caving  in  of  the  wall  of  mines,  the 
life  soon  goes  out. 

In  fact,  without  this  important  element  there  could 

90 


OXYGEN 


91 


be  no  fire ;  there  could  be  no  water ;  there  could  be  no 
life,  and  the  earth  would  be  a  barren  waste. 

Preparation.  One  of  the  simplest  ways  to  obtain 
oxygen  is  to  separate  it  from  some  compound  in  which 
it  is  found,  and  collect  the  gas  by  doAvnward  displace- 
ment of  water.  This  is  done  by  inverting  large  mouth 
bottles  filled  with  water  over  the  bridge  in  a  pneumatic 


Fig.  39.  Preparation  of  oxygen.  A  mixture  of  potassium 
chlorate  and  manganese  dioxide  is  being  heated  in  the  flask. 
The  gas  passes  out  through  the  delivery  tube  and  collects  in 
the  bottles. 


trough  which  is  filled  with  water  to  a  depth  just  cover- 
ing the  bridge.  A  tube  leads  from  the  flask  containing 
the  compound,  to  the  mouth  of  the  bottle  under  the 
•water.  As  the  compound  is  broken  up  and  the  oxygen 
separated  from  it,  usually  by  the  application  of  heat, 
the  gas  being  much  lighter  than  water  rises  into  the 


92  A  YEAR  IN  SCIENCE 

bottle  and  forces  the  water  out.  After  the  bottle  is 
filled  with  oxygen,  it  should  be  removed  with  a  cover 
over  the  mouth  and  kept  right  side  up,  because  oxygen 
is  1.1  times  as  heavy  as  air  and  if  left  inverted  would 
soon  run  out. 

Mercuric  oxide  is  a  compound  sometimes  used  to 
obtain  oxygen.  It  is  a  red  powdery  substance  which, 
when  thoroughly  heated,  separates  into  its  component 
parts,  mercury  and  oxygen: 

Mercuric  oxide  =  mercury  and  oxygen. 

In  this  connection  mercuric  oxide  is  also  of  his- 
torical interest,  for  it  was  with  this  compound  that  in 
1774  Joseph  Priestley,  an  English  scientist,  carried  on 
experiments  that  led  to  the  discovery  of  oxygen. 

When  larger  quantities  of  oxygen  are  desired  potas- 
sium chlorate,  a  compound  containing  a  large  amount 
of  oxygen,  is  used.  It  has  been  found  that  potassium 
chlorate  gives  up  its  oxygen  more  quickly  if  a  black, 
finely  powdered  substance,  manganese  dioxide,  is 
mixed  with  it.  Although  manganese  dioxide  contains 
oxygen,  it  gives  up  none  of  it  in  this  process.  The 
sole  function  of  the  black  powder  is  to  hasten  the 
breaking  up  of  the  potassium  chlorate.  The  change 
which  takes  place  may  be  expressed  as  follows : 

Potassium  chlorate  =  potassium  chloride  +  oxygen. 

Properties.  On  examining  a  bottle  of  pure  oxygen, 
it  will  be  found  colorless,  odorless,  and  tasteless.  It 
is  a  very  active  element  and  combines  readily  with 
many  substances.  With  some  it  combines  so  actively 


OXYGEST  93 

that  both  heat  and  light  are  produced,  and  we  call  the 
process  burning.  If  a  glowing  ember  be  thrust  into  a 
bottle  of  pure  oxygen,  the  ember  at  once  ignites  and 
burns  vigorously.  Charcoal,  which  barely  glows  in 
the  air,  will  glow  intensely  with  an  almost  invisible 
flame  in  the  oxygen.  Sulphur,  which  burns  with 
a  pale  blue  flame  in  the  air,  burns  with  a  brilliant  blue 
flame  in  oxygen.  Even  a  steel  watch  spring,  or  a  ball 
of  steel  wool,  if  dipped  in  sulphur  and  ignited  and 
then  thrust  into  a  jar  of  oxygen,  will  burn  vigorously 
and  throw  off  brilliant  sparks. 

Oxidation.  The  gas  left  in  the  bottle  after  the 
burning  of  the  charcoal  was  carbon  dioxide,  a  color- 
less gas.  The  burning  sulphur  left  behind  a  colorless 
gas,  called  sulphur  dioxide;  and  the  burning  steel 
threw  off  the  brilliant  sparks  which  formed  molten 
globules  of  oxide  of  iron.  From  these  statements  it  is 
apparent  that  oxygen  Combined  with  the  various  ele- 
ments, carbon,  sulphur,  and  iron,  to  form  oxides  of 
these  substances.  In  fact,  oxygen  combines  with  all 
but  a  very  few  of  the  known  elements.  The  process 
of  the  union  of  oxygen  with  some  other  element  or  com- 
pound is  called  oxidation, 

The  product  resulting  from  oxidation  is  a  compound 
called  an  oxide. 

The  above  chemical  phenomena  may  be  expressed  as 
follows : 

Carbon  -j-  oxygen  =  carbon  dioxide 
C  +  2  X  O  =  CO2 


94  A  YEAR  IN  SCIENCE 

Sulphur  +  oxygen  =  sulphur  dioxide 

S  +  2  X  0  =  SO2 
Iron  -f-  oxygen  =  oxide  of  iron  - 

Rapid  oxidation  is  always  accompanied  by  heat  and 
light.  To  fully  appreciate  this  statement  you  need  but 
recall  the  methods  employed  in  heating  our  homes. 
Wood,  coal,  coke,  etc.,  are  burned  in  a  furnace.  Burn- 
ing is  rapid  oxidation.  In  other  words,  the  oxygen  of 
the  air  combines  with  the  carbon  of  the  wood,  coal,  or 
coke,  and  the  home  is  made  comfortable  with  the  heat 
evolved  in  the  process.  If  more  heat  is  desired,  we  in- 
crease the  burning  or  oxidation  by  admitting  more 
oxygen  to  the  fuel  through  the  draughts.  If  less  heat 
is  desired,  the  draughts  are  closed,  admitting  a  smaller 
amount  of  oxygen,  thus  reducing  oxidation. 

If,  however,  oxidation  is  very  slow,  as  in  the  rusting 
.of  iron  or  the  decay  of  wood,  it  is  not  accompanied  by 
any  noticeable  amount  of  heat  or  light,  though  the 
sum  total  of  the  heat  evolved  during  the  process  of 
decay  is  as  much  as  would  be  given  off  were  the  same 
piece  of  wood  completely  burned  in  a  few  minutes. 

Uses.  Oxygen  is  absolutely  necessary  to  life.  Only 
a  few  very  minute  forms  of  plant  life  can  exist  with- 
out it.  Oxidation  goes  on  in  the  bodies  of  living  organ- 
isms in  very  much  the  same  manner  as  it  does  in  the 
furnace.  Of  course,  it  is  not  accompanied  by  light, 
but  the  results  are  the  same.  In  the  process  of  respi- 
ration, oxygen  is  taken  into  the  lungs,  where  some  of 


OXYGEN  95 

it  is  absorbed  into  the  blood.  It  is  then  carried  to  all 
parts  of  the  body  where  the  tissues  are  oxidized  and  the 
oxides,  chiefly  carbon  dioxide,  are  taken  by  the  blood  to 
the  lungs  or  to  other  organs,  where  they .  are  elimi- 
nated. By  heat  evolved  in  the  process  of  oxidation, 
the  bodily  temperature  is  maintained  and  the  energy 
developed  for  thought  and  action. 

Oxygen  is  slightly  soluble  in  water,  about  three 
parts  in  a  hundred.  This  small  amount  supports  all 
the  varied  forms  of  aquatic  life.  As  stated  above, 
all  burning,  all  decay,  are  dependent  upon  oxygen. 
Thus,  in  this  way,  oxygen  serves  as  a  purifying  agent, 
for  all  dead  animal  and  vegetable  products  are  slowly 
oxidized  and  thus  changed  into  harmless  substances. 

Oxygen  is  also  used  by  the  physician  in  instances 
where  the  patient  is  unable  to  inhale  a  sufficient 
amount  from  the  air. 

Source.  From  the  fact  that  oxygen  combines  so 
readily  with  so  many  different  substances,  it  would 
seem  that  the  supply  would  eventually  be  exhausted. 
However  great  the  oxidation,  the  proportion  of  oxygen 
in  the  air  is  not  much  affected,  for  all  green  plants 
are  continually  giving  back  to  the  air  oxygen,  which 
is  thrown  off  in  the  process  of  food  making  in  the 
plant. 

Questions 

1.  Who  was  Joseph  Priestley?   What  is  his  claim, 
to  fame? 

2.  Name  the  chief  properties  of  oxygen. 


96  A  YEAR  IN  SCIENCE 

3.  Can  you  suggest  any  reason  why  practically  all 
the  oxygen  of  the  earth  is  locked  up  in  water  and  in  the 
compounds  which  make  up  the  rocks  ? 

4.  What  keeps  up  the  amount  of  oxygen  in  the 
air  when  it  is  constantly  being  used  up  by  burning  ? 

5.  A  flame  is  a  burning  gas.     Why  do  not  pure 
charcoal  and  iron  wire   burn  with  a  flame   in  pure 
oxygen  ? 

6.  Name  three  different  ways  to  obtain  free  oxygen 
in  the  laboratory. 

7.  What  is  burning?    Oxidation?    An  oxide? 

8.  What  is  the  significance  of  opening  the  draught 
in  the  furnace? 

9.  What  oxidations  are  valuable?    What  oxidations 
does  man  cause  to  occur  for  his  comfort  ?    Mention  others 
which  man  wishes  to  prevent. 

10.  Describe  as  well  as  you  can  the  condition  of 
things  if  the  atmosphere  were  pure  oxygen.     Judge 
from  your  knowledge  of  the  activity  of  oxygen. 

11.  How    is    the    balance    of    oxygen    in    the    air 
maintained  ? 


CHAPTER  XIV 

HYDROGEN 

(Hydrogen  =  H) 

Occurrence.  Although  hydrogen  is  found  widely 
distributed  in  combination  with  other  elements,  it  is 
found  but  rarely  in  the  free  state.  It  is  sometimes 
found  free  among  the  gases  expelled  from  volcanoes, 
in  meteorites,  and  a  trace  of  it  is  found  in  the  air. 

Hydrogen  makes  up  11%  of  water,  which  covers 
nearly  three-fourths  of  the  earth.  It  is  found  as  a 
constituent  part  of  natural  gas  and  the  oils  obtained 
from  the  earth  as  fuel,  and  forms  a  part  of  all  vege- 
table and  animal  matter. 

Preparation.  Hydrogen  may  be  obtained  either 
from  water  or  from  any  acid,  of  which  substances  it 
forms  an  essential  part.  Water  is  a  compound  of 
hydrogen  and  oxygen.  If  an  electric  current  is  passed 
through  water  to  which  a  small  amount  of  acid  has 
been  added,  it  may  be  separated  into  its  component 
parts,  oxygen  and  hydrogen.  The  method  commonly 
used  in  the  laboratory  is  to  separate  the  hydrogen 
from  some  acid.  Some  metal,  as  zinc  or  iron,  is  used 
for  this  purpose. 

Place  a  few  small  pieces  of  zinc  in  a  flask  and  close 

97 


98 


A  YEAR  IN  SCIENCE 


the  flask  with  a  rubber  stopper,  fitted  with  a  thistle 
tube  through  which  acid  may  be  poured  into  the  flask, 
and  a  short  glass  delivery  tube  through  which  the 


Fig".    40. 


Preparation    of  hydrogen   from   hydrochloric   acid   and 
zinc. 


gas  may  escape.  When  the  zinc  comes  in  contact  with 
the  acid,  a  chemical  action  takes  place  by  Which 
hydrogen  is  set  free.  Any  acid  will  do,  though  hydro- 
chloric acid  is  the  one  most  generally  used.  Hydro- 
chloric acid  is  a  compound  of  the  elements  chlorine 
and  hydrogen.  When  the  acid  and  the  metal  come  in 
contact,  the  metal  displaces  the  hydrogen  and  com- 
bines with  the  chlorine  to  form  zinc  chloride. 
Zinc  +  hydrochloric  acid  =  zinc  chloride  +  hydrogen. 

Zn  +  2HC1  =  ZnCl2  +  2H. 

The  freed  gas  escapes  through  the  delivery  tube  and 
may  be  collected  by  downward  displacement  of  water, 
as  was  oxygen. 

The  gas  from  the  generator  should  be  allowed  to 
escape  until  you  feel  sure  that  all  the  air  that  was  in 
the  flask  and  tubes  has  escaped.  Great  care  must  be 


HYDROGEN  99 

exercised  not  to  bring  a  flame  near  a  mixture  of  oxy- 
gen and  hydrogen,  for  if  the  mixture  is  lighted  an 
explosion  will  surely  follow.  So  every  care  must  be 
taken  to  free  the  hydrogen  from  air  before  it  is 
lighted. 

Properties.  Hydrogen  is  a  colorless,  odorless,  taste- 
less gas.  It  is  the  lightest  known  gas  and  because  of  this 
fact  it  is  used  as  the  standard  of  weight  by  which  all 
gases  are  measured.  In  speaking  of  the  weight  of  any 
other  gas  it  is  spoken  of  as  being  so  many  times  as 
heavy  as  hydrogen.  Thus  air  is  14.4  times  as  heavy, 
and  oxygen  16  times  as  heavy  as  hydrogen.  It  com- 
bines readily  with  oxygen,  burning  with  a  pale  blue 
flame.  If  a  burning  splinter  be  brought  to  the  mouth 
of  an  inverted  bottle  of  hydrogen,  a  slight  explosion 
will  occur  and  a  pale  blue,  almost  invisible  flame 
will  burn  upward  into  the  bottle.  This  is  the  test  of 
hydrogen.  If  the  burning  splinter  is  thrust  quickly 
into  the  hydrogen  an  explosion  occurs  at  the  mouth 
of  the  bottle,  but  the  flame  on  the  splinter  will  be 
extinguished.  This  shows  that  hydrogen  will  burn, 
but  will  not  support  combustion. 

Although  it  is  not  poisonous  to  breathe  hydrogen, 
one  could  not  live  long  with  only  hydrogen,  as  oxygen 
is  necessary  to  life. 

Uses.  Because  of  its  lightness,  hydrogen  is  used 
sometimes  in  filling  balloons,  though  hot  air  and  coal 
gas  are  more  frequently  used  because  they  are 
cheaper.  In  recent  years  hydrogen  has  been  used  in 


100  A  YEAR  IN  SCIENCE 

air  ships  because  of  its  lifting  power.  Hydrogen  is 
also  important  as  a  fuel.  A  number  of  mixtures  of 
combustible  gases,  consisting  largely  of  carbon  com- 
pounds and  hydrogen,  are  used  extensively  for  the 
production  of  light  and  heat.  Those  chiefly  used  are 
coal  gas,  water  gas,  natural  gas,  and  acetylene. 


Questions 

1.  Is  hydrogen  found  in  the  free  state  in  nature? 

2.  How  may  pure  hydrogen  be  obtained? 

3.  When    generating   hydrogen,    why    should   the 
first  gas  always  be  allowed  to  escape  from  the  end  of 
the  tube? 

4.  What  are  the  chief  properties  of  hydrogen  ? 

5.  What  use  is  made  of  the  fact :   (1)  that  hydrogen 
is  a  very  light  gas,  (2)  that  it  unites  energetically  with 
oxygen,  giving  out  much  heat,   (3)   that  it  is  a  con- 
stituent of  oil  and  natural  gas,  (4)  that  it  is  very  hard 
to  liquefy  it? 


CHAPTER  XV 

NITROGEN 

(Nitrogen  =  N) 

Occurrence.  Nitrogen  is  another  element  that  plays 
an  important  part  in  plant  and  animal  life.  In  com- 
bination with  carbon,  hydrogen,  and  oxygen,  it  forms 
protein,  one  of  the  main  classes  of  foodstuffs.  It  is 
an  essential  constituent  of  all  living  organisms.  It  is 
also  found  in  nature  in  the  form  of  potassium  nitrate, 
a  compound  commonly  called  niter,  from  which  fact  it 
derives  its  name.  As  an  element  it  forms  about  four- 
fifths  of  the  air. 

Preparation.  For  class  use  nitrogen  is  usually 
obtained  from  the  air. 
Since  oxygen  and  nitro- 
gen make  up  more  than 
99%  of  the  atmosphere, 
when  oxygen  is  removed, 
nitrogen  is  left  sufficiently 
pure  for  the  study  of  its 
physical  properties.  Oxy- 
gen is  removed  by  combin- 
bining  it  with  any  element 
whose  oxide  is  readily 


Fig.  41.  Experiment  to  determine 
the  composition  of  air. 


101 


102  4  VKAR  IX  SCIENCE 

absorbed  by  water.  For  this  purpose  phosphorus 
is  most  generally  used.  After  filling  the  pneumatic 
trough  with  water  to  the  depth  of  two  inches,  float 
a  small  piece  of  cork  on  it.  Place  on  the  cork 
with  forceps  a  piece  of  yellow  phosphorus  about 
the  size  of  a  small  pea.  After  igniting  the  phosphorus, 
quickly  invert  a  belljar  over  it  so  as  to  confine  a 
portion  of  the  air.  The  phosphorus  will  burn  as  long 
as  there  is  any  oxygen  in  the  jar,  forming  a  white 
cloud  of  solid  particles,  oxide  of  phosphorus.  During 
the  next  twenty  or  thirty  minutes  this  cloudy  oxide 
will  be  absorbed  by  the  water,  and  the  gas  remaining 
in  the  jar  is  nitrogen. 

Nitrogen  may  also  be  prepared  by  taking  a  mixture 
of  8  grams  of  sodium  nitrite  and  3  grams  of  ammon- 
ium chloride,  to  which  is  added  about  15  c.c.  of  water 
heated  gently  below  the  boiling  point  of  water.  In  the 
chemical  action  resulting  between  these  compounds, 
nitrogen  is  liberated,  which  may  be  collected  as  were 
oxygen  and  hydrogen. 

Properties.  Nitrogen  is  a  colorless,  odorless,  tasteless 
gas.  That  it  is  very  inactive  may  be  seen  by  insert- 
ing a  burning  splinter  into  a  bottle  of  the  gas.  The 
flame  is  extinguished  at  once.  Nitrogen  neither  burns 
nor  supports  combustion.  Because  of  its  inactivity  it 
is  only  with  the  greatest  difficulty  that  it  can  be  made 
to  unite  directly  with  any  substance. 

Uses.  The  very  great  inactivity  of  nitrogen  might 
lead  one  to  think  it  of  little  use  in  nature.  It  is  in 


NITROGEN  103 

that  very  characteristic,  however,  that  much  of  its 
value  lies.  We  have  seen  how  very  rapid  oxidation  is 
in  pure  oxygen.  An  atmosphere  of  pure  oxygen 
would  be  almost  as  disastrous  as  one  with  no  oxygen. 
A  mixture  of  oxygen  with  a  harmless,  inactive  gas 
which  will  hold  the  oxygen  in  check  is  necessary. 
This  seems  to  be  the  chief  use  of  nitrogen.  Forming 
as  it  does  about  four-fifths  of  the  air,  it  dilutes  the 
other  one-fifth,  which  is  oxygen,  and  thereby  guards 
against  too  rapid  oxidation,  and  consequently  wide- 
spread destruction. 

Nitrogen  is  necessary  to  plant  life,  and  although  it 
forms  a  large  part  of  the  air,  plants  are  unable  to  use 
it  in  the  free  state.  They  obtain  the  element  from  the 
soil  from  some  soluble  compound  of  nitrogen,  usually 
a  nitrate.  If  for  some  reason  these  compounds 
become  insufficient  in  the  soil  for  the  proper  growth 
of  plants,  they  must  be  restored  in  some  way.  This 
is  done  by  nitrogenous  fertilizers,  such  as  nitrate  of 
soda  (Chili  saltpetre)  and  sulphate  of  ammonia. 

Nitrogen  is  used  commercially  in  compound  form 
in  the  manufacture  of  ice.  Nitrates  are  also  of  great 
commercial  value  in  the  making  of  explosives,  gun- 
powder, dynamite,  and  nitro-glycerin. 

Questions 

1.  Name  the  properties  of  nitrogen. 

2.  What  are  the   chief  sources  of  nitrogen? 

3.  State  two  ways  of  preparing  it  for  class  use. 


104  A  YEAR  IN  SCIENCE 

4.  What  are  the  chief  uses  of  nitrogen? 

5.  What    proportion    by    volume    of    the    air    is 
nitrogen  ? 

6.  Which  is*  more  important  in  the  air,  oxygen  or 
nitrogen  ? 

7.  What  would  probably  result  if  the  balance  in 
either  direction  were  very  much  disturbed? 

8.  Oxygen    is    16    times    as    heavy    as    hydrogen, 
nitrogen  is  14  times  as  heavy  as  hydrogen.     Air  is  J 
oxygen  and  f  nitrogen  by  volume.     How  many  times 
as  heavy  is  a  quart  of  air  than  a  quart  of  hydrogen? 

9.  From    Avhat    source    do    most    plants    obtain 
nitrogen? 

10.     What  is  a  nitrogenous  fertilizer  ? 


CHAPTER  XVI 

ACIDS,    BASES,    AND    NEUTRAL    SUBSTANCES 

Introduction.  In  every  kitchen  may  be  found  three 
things:  vinegar,  ammonia,  and  common  salt.  They 
are  three  examples  of  three  great  classes  of  com- 
pounds. Vinegar  belongs  with  the  acids.  Ammonia 
belongs  with  the  bases.  Common  salt  belongs  with  the 
general  group  of  salts. 

Acids.  There  are  many  acids  with  which  you  are 
already  familiar.  There  is  not  a  boy,  at  least,  who 
does  not  know  of  the  sour,  puckery  juice  of  a  green 
apple.  The  grape,  the  peach,  the  plum,  and  practi- 
cally all  other  fruits  are  characterized  in  their  early 
stages  by  their  distinctly  acid  taste.  The  lime,  the 
lemon,  and  some  other  fruits  retain  this  acid  even 
in  the  ripened  form.  Sweet  cider  when  exposed  to 
the  air  becomes  sour  and  acid.  Most  of  the  acids 
which  we  know  in  the  home  come  from  the  plant 
world.  There  are  other  acids,  however,  wrhich  are 
prepared  and  used  in  almost  countless  processes  in 
shops  and  factories.  The  three  most  important  of 
these  are  hydrochloric  acid,  sulphuric  acid,  and  nitric 
acid. 

105 


106  A  YEAR  IN  SCIENCE 

Characteristics  of  acids.  Much  as  the  acids  may 
vary  in  their  individual  qualities,  they  all  possess 
certain  qualities  in  common. 

They  all  contain  hydrogen.  Hydrochloric  acid,  for 
example,  is  composed  of  hydrogen  and  chlorine, 
H  +  Cl  =  HC1.  Nitric  acid  is  composed  of  hydrogen, 
nitrogen,  and  oxygen,  HN03;  and  sulphuric  acid,  of 
hydrogen,  sulphur,  and  oxygen,  H2S04. 

They  all  have  a  sour  taste. 

The  most  valuable  test  by  which  acids  may  be  recog- 
nized comes  from  their  action  upon  a  certain  vegetable 
substance  known  as  litmus.  Paper  colored  by  this 
substance  is  known  as  litmus  paper,  and  it  is  used  as  the 
common  test  for  an  acid.  Acids  turn  blue  litmus  to  a 
red  color. 

Bases.  Bases  are  substances  with  which  we  do  not 
so  frequently  come  in  contact.  Mention  has  already 
been  made  of  ammonia.  In  the  laboratory  the  bases 
most  commonly  used  are  sodium  hydroxide  and  potas- 
sium hydroxide.  These  are  white  solids,  soluble  in 
water. 

Characteristics  of  bases.  Bases,  like  acids,  have 
certain  distinguishing  characteristics.  All  bases  con- 
tain hydrogen  and  oxygen.  For  example,  sodium 
hydroxide  contains  sodium,  hydrogen,  and  oxygen, 
NaOH.  Potassium  hydroxide  contains  potassium, 
hydrogen,  and  oxygen,  KOH. 

A  solution  of  a  base  has  a  soapy  feel  and  taste. 


ACIDS,  BASES,  NEUTRAL  SUBSTANCES  1Q7 

It  reverses  the  color  change  produced  by  acids. 
Bases  turn  red  litmus  paper  blue. 

Neutralization.  If  the  right  amount  of  hydrochloric 
acid  is  mixed  with  the  right  amount  of  sodium  hy- 
droxide, a  base,  all  properties  of  both  the  acid  and  the 
base  disappear.  The  resulting  substance  does  not 
have  a  sour  taste,  or  a  soapy  feeling,  and  it  does 
not  have  any  action  at  all  on  litmus  paper.  The  acid 
has  neutralized  the  base,  and  the  base  has  neutralized 
the  acid.  All  the  distinguishing  acid  and  basic  prop- 
erties have  gone.  If  the  solution  of  the  acid  and  the 
base  is  evaporated  a  white  powder  remains.  If  this 
is  tasted,  it  will  be  found  to  be  common  table  salt.  The 
liquid  evaporated  was  water.  When  an  acid  is  added 
to  a  base,  the  product  formed  is  a  salt  and  water. 
This  may  be  written  in  the  form  of  the  equation: 

acid  +  base  =  salt  +  water. 

This  action  of  an  acid  011  a  base  is  called  neutralization. 
Salts.  The  products  of  neutralization  are  a  salt  and 
water.  Salts  as  a  class  have  no  particular  taste.  They 
have  no  action  at  all  on  red  or  blue  litmus  paper  and 
hence  are  known  as  neutral  substances.  Not  all  neutral 
substances  are  salts,  however.  For  example :  water, 
alcohol,  and  milk  are  neutral  substances,  but  they  are 
not  salts. 

Acid  4-  Base  =  Salt  +  Water. 
H  Cl  +  NaOH  =  Na  Cl  +  H2O. 
H  N03  -f  NaOH  —  Na  NO3  -f  H2O. 
H,SO4  -f-  2NaOH  =  Na.,SO4  +  2H,0. 


]()8  A  YEAR  IN  SCIENCE 

These  equations  indicate  the  reactions  which  take 
place  in  the  process  of  neutralization.  In  each 
case  the  name  of  the  salt  is  derived  from  the  names  of 
the  acid  and  the  base  used  in  its  production.  Hydro- 
chloric acid  and  sodium  hydroxide  produce  common 
table  salt,  sodium  chloride ;  nitric  acid  and  sodium  hy- 
droxide produce  Chili  saltpetre,  sodium  nitrate;  sul- 
phuric acid  and  sodium  hydroxide  produce  Glauber's 
salt,  sodium  sulphate. 


Questions 

1.  Name  three  foods  which  contain  acids. 

2.  How  do  you  know  these  foods  contain  acids  ? 

3.  How  does  the   amount  of  acid  in   green  fruit 
compare  with 'that  in  ripe? 

4.  Name  three  acids  frequently  used  in  commercial 
processes. 

5.  State  three  characteristics  common  to  all  acids. 

6.  What  is  the  source  of  litmus? 

7.  What  is  the  test  for  an  acid? 

8.  What    is    the    symbol    for    hydrochloric    acid? 
Nitric  acid?     Sulphuric  acid? 

9.  Name  three  bases. 

10.  What  is  the  appearance  of  sodium  hydroxide? 
Potassium  hydroxide  ? 

11.  Write  the  symbols  for  two  bases. 

12.  What  are  the  principal  characteristics  of  bases  \ 

13.  What  is  the  test  for  a  base? 

14.  How  does  a  neutral  substance  differ  from  an 
acid  and  from  a  base? 


ACIDS,  BASES,  NEUTRAL  SUBSTANCES  1Q9 

15.  How  can  a  neutral  substance  be  made  from  an 
acid  and  a  base? 

16.  How  can  you  obtain  common  salt  from  hydro- 
chloric acid  and  sodium  hydroxide? 

17.  What  are  the  products  of  neutralization? 

18.  Name  three  salts. 

19.  Complete  the  following  equations: 

HC1  +  NaOH  =  ? 
HN03  +  NaOH=  =  ? 
H2SO"4  +  2XaOH  =  ? 

20.  Are  all  neutral  substances  salts? 

21.  Name  three  neutral  substances  which  are  not 
salts. 

22.  How  is  the  name  of  a  salt  derived? 


CHAPTER  XVII 

WATER 

( Water  =  H20) 

Introduction.  Of  all  substances  on  the  surface  of  the 
earth,  water  is  by  far  the  most  abundant. 

In  the  liquid  form  it  makes  up  the  oceans,  lakes,  seas, 
rivers,  springs,  and  brooks,  while  the  air  holds  vast 
quantities  of  it  in  the  gaseous  form.  Add  to  this  the 
vast  stretches  of  ice  and  snow  of  the  polar  regions,  and 
one  soon  realizes  the  truth  of  the  statement,  "  three- 
fourths  of  the  earth's  surface  is  covered  with  water." 

Composition.  For  a  long  time  water  was  regarded 
as  an  element.  However,  toward  the  close  of  the 
eighteenth  century  it  was  proved  to  be  a  compound  of 
the  two  elements,  hydrogen  and  oxygen. 

This  can  be  shown  in  two  ways.  First,  by  breaking 
up  the  compound  into  its  elements  with  the  electric  cur- 
rent; and,  second,  by  combining  the  two  elements  by 
ignition. 

Take  an  electrolysis  apparatus,  such  as  is  shown  in 
Figure  42,  and  fill  the  burettes  with  water  containing  a 
small  amount  of  sulphuric  acid.  Each  arm  of  the  appa- 
ratus holding  the  burette  is  closed  at  the  bottom  with 
a  rubber  stopper,  through  which  passes  a  glass  tube 

110 


WATER 


111 


holding  a  wire  with  a  piece  of  platinum  extending  into 
the  arm,  and  a  free  end  projecting  outward.  To  the 
projecting  wires  attach  the  wires 
leading  from  the  source  of  the  elec- 
tricity and  turn  on  the  current.  As 
soon  as  the  current  passes,  bubbles 
of  gas  rise  from  the  pieces  of  plati- 
num to  the  upper  parts  of  the  tubes. 
The  gas  in  one  tube  collects  just 
twice  as  rapidly  as  in  the  other.  If 
the  gas  in  each  tube  is  tested,  the 
tube  with  the  smaller  quantity  will 
be  found  to  contain  oxygen,  while 
the  other  tube  with  twice  as  much 
volume  will  be  found  to  contain 
hydrogen. 

Thus  the  formula,  water  =  H20. 

Again,  if  oxygen  and  hydrogen 
gases  are  mixed  in  a  dry  vessel  and 
then  ignited,  vapor  collects  on  the 
sides.  This  vapor,  resulting  from 
the  explosion  or  union  of  oxygen 
and  hydrogen,  is  the  oxide  of  hydro- 
gen, or  water. 

Properties  and  uses.  Pure  water  is  an  odorless  and 
tasteless  liquid.  In  thin  layers  it  appears  colorless, 
though  in  larger  bulk  it  has  a  bluish  tinge.  At  ordinary 
pressure  it  boils  at  100° C.  (212°F.)  and  freezes  at 
0°C.  (32°F.)  Most  substances  contract  upon  cooling. 


i 


F  i  g.  42.  D  e- 
composition  of 
water.  An  electric 
current  passed 
through  the  water 
in  the  tubes  decom- 
poses it  into  hydro- 
gen and  oxygen. 


112  A  YEAR  IN  SCIENCE 

Water,  as  you  have  learned,  contracts  upon  cooling 
until  4°C.  (39°F.)  is  reached,  then  it  begins  to  expand. 
One  hundred  cubic  feet  of  water,  as  ice,  will  require 
one  hundred  and  nine  cubic  feet  of  space.  Thus  as 
water  freezes  a  layer  of  ice  spreads  over  the  surface  of 
the  water,  Avhile  the  life  underneath  continues  un- 
molested. 

The  expansive  force  of  freezing  water  will  be  under- 
stood if  you  will  recall  what  happens  to  the  pipes  when 
the  water  in  them  freezes.  The  freezing  water  expands, 
and  as  the  pipe  does  not  expand  and  the  ice  must  have 
more  room,  the  pipe  bursts. 

Perhaps  you  have  noticed  the  " fluffed  up"  appear- 
ance of  the  garden  soil  in  the  spring  just  before  the 
frost  has  gone  out  of  it.  During  the  fall  and  winter, 
the  water  from  rains  and  snow  trickled  down  into  the 
earth  and  later  froze.  Ice  requires  about  one-eleventh 
more  space  than  liquid  water,  and  as  the  water  in  the 
crevices  and  cracks  in  the  soil  froze  it  required  more 
room.  The  pressure  thus  exerted  pushed  up  the  sur- 
face soil,  giving  it  the  fluffy  appearance.  This  is  a 
great  boon  to  the  farmer,  as  it  helps  to  pulverize  the  soil. 
On  rocky  hills  and  mountain  sides,  this  form  of  weath- 
ering is  making  neiv  soil  by  splitting  off  particles  of 
rock,  which  are  carried  to  the  base  of  the  mountain 
with  each  rain. 

Another  great  use  of  water  is  its  power  of  solution. 
If  a  spoonful  of  sugar  is  placed  in  a  glass  of  water,  the 
sugar  disappears.  It  has  been  dissolved  by  the  water. 


WATER 


113 


Photograph  "by  Detroit  Publishing  Co. 

Fig.  43.     Summit  of  Pike's -Peak,  showing  rock  fragments  split  off 
principally  by  alternating  heat  and  cold. 

That  it  is  present  in  the  water  is  recognized  by  its 
sweetened  taste,  and  may  also  be  shown  by  evaporating 
the  water,  when  the  sugar  again  appears  in  the  solid 
form  at  the  bottom  of  the  vessel.  Some  substances  that 
are  not  dissolved  in  water  may  be  held  in  suspension, 
giving  to  the  water  the  color  of  the  substances  thus 
held. 

When  starch  and  water  are  shaken  together  in  a 
tube,  the  starch  does  not  dissolve,  but  its  particles  are 
held  in  suspension,  giving  to  the  water  a  milky  white 
appearance. 

After  every  rain  the  water  of  the  small  streams  is  of 
muddy  color.  This  is  due  to  the  particles  of  soil  the 


114  A  YEAR  IN  SCIENCE 

water  is  carrying  along.  Floods  are  dreaded  and  leave 
much  destruction  in  their  wake,  and  yet  the  productive 
river  bottoms  owe  their  fertility  to  the  mineral  sub- 
stances brought  in  solution  and  the  new  layers  of  soil 
left  by  the  flood. 


Permission  United  States  Geological  Survey. 
FIG.   44.     View  of  Delaware  water  gap,  a  productive  river  valley. 

Hard  and  soft  water.  The  terms  hard  and  soft  water 
are  in  common  use  in  the  home.  You  know,  too,  that 
hard  water  lathers  soap  only  with  difficulty,  while  soft 
water  lathers  it  freely.  On  this  basis  we  can  classify 
rain  water  as  soft  water,  while  water  from  the  spring  or 
well  is  hard.  Since  all  spring  and  well  water  were  once 
rain  water,  it  is  evident  that  they  have  become  hard  in 
passing  through  the  earth.  The  hardness  is  due  to  the 
mineral  substances  held  in  solution  by  the  water.  Some- 
times hard  water  becomes  soft  after  boiling.  The  minerals 
held  in  solution  are  deposited  on  the  bottom  of  the  vessel, 


WATER  115 

as  in  the  tea  kettle,  and  if  this  deposit  is  tested  with 
hydrochloric  acid,  it  will  be  found  to  be  a  carbonate  of 
lime.  On  the  other  hand,  some  water  is  not  changed 
by  boiling,  in  which  case  either  calcium  sulphate  or 
magnesium  sulphate  is  present,  or  both  may  be  present. 
Water  of  this  kind  is  rendered  soft  only  by  chemical 
means. 

Hard  water  is  more  expensive  for  cleansing  than  soft 
water,  because  the  soap  used  to  soften  it  is  wasted  as 
far  as  cleansing  is  concerned. 

Plant  and  animal  life  dependent  upon  water.  The 
service  of  water  to  plant  and  animal  life  cannot  be  over- 
estimated. Most  of  the  food  used  by  plants  comes 
from  minerals  in  the  soil.  For  these  they  are  absolutely 
dependent  upon  water,  as  the  plant  can  obtain  its  food 
from  the  soil  only  in  solution.  As  water  sinks  within 
the  earth  it  dissolves  from,  the  soil  much  of  the  food 
materials,  which  are  absorbed  by  the  fine  root  hairs  into 
the  plant. 

Water  is  also  vitally  necessary  to  all  animal  life. 
Before  food  can  be  absorbed  into  the  blood  it  must  be 
dissolved  and  reduced  to  a  thin  liquid.  Also  the  broken 
down  wastes  of  the  body  must  be  dissolved  to  be 
absorbed  into  the  blood,  and  carried  to  the  eliminating 
organs.  The  system  must  be  kept  constantly  flushed 
to  eliminate  the  waste  and  poisonous  matters  from  the 
body  if  one  is  to  remain  vigorous  and  active. 

Water  applied  freely  within  and  on  the  exterior  of 
the  body  will  prevent  the  accumulation  of  the  waste 


A  YEAR  IN  SCIENCE 

matters  which  nature  must  eliminate.  Through  the 
lungs  and  kidneys,  the  average  person  excretes  about 
four  pints  of  water  per  day. 

Thus  the  demand  for  fresh  water  is  constant.  This 
is  not  entirely  supplied  by  the  water  we  drink,  for  the 
greater  part,  by  weight,  of  many  of  our  solid  foods  is 
water.  Thus  potatoes  contain  78%  water,  milk  85%  , 
beef  over  50%,  tomatoes  and  asparagus  94%,  while 
some  fruits,  such  as  strawberries  and  watermelons,  are 
over  nine-tenths  water.  Bread  probably  contains  as 
little  water  as  any  of  our  common  foods,  and  it  is  about 
35%  water. 

Dangers  in  water.  Pure  water  is  practically  un- 
known. Owing  to  its  solvent  action,  all  water  that 
passes  through  the  soil  carries  more  or  less  mineral 
substances  or  gases  in  solution.  The  peculiar  taste  or 
odor  of  the  water  from  a  mineral  spring  is  due  to  the 
substance  the  water  holds  in  solution.  Even  rain 
water,  which  is  water  that  has  been  evaporated  from 
the  surface  of  the  earth  into  the  higher  atmosphere  and 
then  sent  back  again,  is  not  pure.  In  its  passage 
through  the  air  it  carries  along  with  it  the  small  dust 
particles  it  encounters  and  it  probably  absorbs  some 
gases  from  the  air.  The  substances  thus  far  mentioned 
are  not  necessarily  harmful.  Indeed,  the  dissolved  min- 
erals are  necessary  to  plant  and  animal  life.  ^But 
bacteria  are  found  practically  everywhere,  on  the  sur- 
face of  the  earth  and  in  the  air.  It  is  when  the  harm- 
ful bacteria  get  into  drinking  water  that  it  becomes  a 


WATER  117 

menace  to  health.  Epidemics  of  typhoid  fever,  scarlet 
fever,  and  cholera  have  been  traced  to  drinking  water 
that  had  become  contaminated  with  the  forms  that  pro- 
duce these  diseases.  Our  city  governments  keep  a  close 
watch  on  the  water  supply  to  protect  the  inhabitants 
from  the  dangers  of  polluted  water. 

Filtering  water  is  a  wise  precaution,  if  one  is  careful 
to  cleanse  the  filter  frequently,  as  it  reduces  the  dan- 
gers from  pollution  to  a  minimum. 

When  water  is  under  suspicion  it  is  wise  to  boil  it 
before  using.  Fifteen  minutes'  boiling  destroys  all 
living  forms  in  the  Avater  and  renders  it  safe  for 
drinking.  True,  boiled  water  has  a  flat  taste,  because 
the  air  which  was  held  in  solution  was  driven  off  in 
the  boiling,  but  this  can  be  overcome  partly,  at  least, 
by  filling  sterilized  bottles  half  full  with  boiled  water, 
and  mixing  the  air  and  water  by  shaking.  The  bottles 
should  then  be  closed  and  set  in  a  cool  place  until 
ready  for  use. 

The  following  method  of  purifying  any  drinking 
water  so  that  it  will  be  safe  to  drink  is  given  by  Dr. 
W.  A.  Evans,  former  Health  Commissioner  of  Chicago : 

"Take  a  level  teaspoonful  of  chloride  of  lime  and 
rub  it  up,  until  there  are  110  lumps,  in  a  teacup  of  water. 
Dilute  this  with  three  cupfuls  of  water,  and  keep  this 
stock  solution  in  a  stoppered  bottle  for  use.  A  tea- 
spoonful  of  this  stock  solution,  added  to  a  two-gallon 
pail  of  water,  and  well  stirred  up,  will  destroy  all 
typhoid  or  other  dysentery  producing  germs  in  ten 


118  A  YEAR  IN  SCIENCE 

minutes,  and  will  make  the  water  safe  to  drink.  If 
this  quantity  makes  the  water  taste,  use  a  little  less, 
otherwise  not.  Get  the  chloride  of  lime  in  metallic 


Questions 

1.  Is  water  an  element  or  a  compound? 

2.  In  what  two  ways  can  this  be  shown? 

3.  How  long  has  this  fact  been  known? 

4.  Give  the  chemical  formula  for  water. 

5.  Name  the  most  essential  physical  properties  of 
water. 

6.  How  does  water  differ  from  most  substances 
when  cooled  below  4C  C.  ? 

7.  Of    what    advantages    is    this    peculiarity    in 
nature's  plan? 

8.  How    do    you    account    for    the    "fluffed    up" 
appearance  of  the  garden  soil  early  in  the  spring? 

9.  How  does  water  help  to  enrich  the  soil? 

10.  What  is  meant  by  hard  water? 

11.  How  may  hard  water  be  rendered  soft? 

12.  Explain  fully  the  role  of  water  in  the  life  of 
most  plants  and  animals. 

13.  What    danger    is    there    in    drinking    surface 
water  ? 

14.  Of  what  advantage  is  filtered  water? 

15.  Why     is     it     necessary     to     clean     the     filter 
frequently  ? 

16.  How   may   water  that   is   under   suspicion,   be 
rendered  safe  for  drinking  purposes? 

17.  Why  should  the  citizens  of  a  community  heed 
carefully  the  warnings  of  the  Board  of  Health  or  the 


WATER  119 

City  Bacteriologist   concerning  the   condition   of  the 
city's  water? 

18.  When  camping  or  traveling  in  the  country,  it  is 
unwise  to  drink  from  a  spring  or  well.    To  make  sure 
that  the  water  is  safe  to  drink,  follow  the  method  of 
purifying  the   drinking  Avater   given   by   Dr.   W.   A. 
Evans  (See  page  117). 

19.  Name   two   substances   which   will   dissolve   in 
water. 

20.  Why  does  water  in  streams  look  muddy  after 
rains  or  heavy  winds? 

21.  Why  are  river  bottoms  usually  very  fertile? 

22.  Do  we  obtain  water  from  our  solid  foods?    Give 
examples. 


CHAPTER  XVIII 

ATMOSPHERE 

Introduction.  Fish  live  in  an  ocean  of  Avater,  but 
just  as  truly  do  we  live  in  an  ocean  of  gas,  which  we 
call  the  atmosphere.  This  atmosphere  which  envelops 
us  at  all  times  extends  more  than  two  hundred  miles 
above  us. 

No  part  of  our  environment  is  of  more  immediate  im- 
portance to  us  than  the  air  we  breathe.  If  it  is  pure 
we  are  strong.  If  we  are  deprived  of  air  for  but  a 
single  hour  we  die. 

Perhaps  no  other  part  of  our  environment  has  had  so 
great  an  influence  in  our  development.  How  we  dress, 
Avhat  we  grow,  and  what  we  eat  are  chiefly  determined 
by  tfee  conditions  of  the  atmosphere,  with  reference  to 
its  temperature,  moisture,  and  winds. 

We  are  not  always  conscious  of  the  air  around  us. 
We  know  roughly  that  on  certain  days  the  air  seems 
heavy,  while  at  other  times  we  feel  its  bracing  effect. 
Generally  it  is  quiet  and  we  are  utterly  unconscious  of 
it ;  at  other  times  we  are  very  much  aware  of  it,  because 
of  its  heavy  winds. 

Our  atmosphere  is  thus  at  one  time  heavy ;  at  another 
time  hot  and  oppressive,  or  cold  and  invigorating.  At 
one  time  it  is  almost  quiet,  and  at  another  traveling  at 

120 


ATMOSPHERE  121 

the  rate  of  over  fifty  miles  an  hour,  forming  a  furious 
gale. 

Such  variations  constantly  occur  on  the  same  level. 
Change  the  level  and  other  variations  occur.  Ascend 
a  lofty  mountain  and  the  air  becomes  rarer  and  rarer, 
until  men  on  such  heights  gasp  for  breath  to  gain  suffi- 
cient oxygen  to  feed  the  body  fires. 

Composition.  The  composition  of  the  atmosphere  is 
nearly  the  same  at  all  times  and  at  all  places  where  it 
has  been  analyzed.  It  is  made  up  chiefly  of  two  gases, 
nitrogen  and  oxygen.  Besides  these  two  gases,  several 
lesser  constituents  are  present.  Of  these,  the  most 
important  are  carbon  dioxide  and  argon.  Water  vapor 
and  dust  are  also  present  in  amounts  which  are  ex- 
tremely variable. 

Air  is  essentially  a  mechanical  mixture.  The  gases 
in  it  are  not  united  or  combined  in  any  way,  but  are 
almost  independent  of  one  another,  and  each  of  them 
retains  its  own  qualities  in  the  mixture.  The  composi- 
tion of  air,  according  to  Kahlenberg,  follows: 

COMPOSITION  OF  AIR 

Per  Cent  of 
Gas  Volume 

Nitrogen    77.42 

Oxygen 20.77 

Water  vapor   (average) 0.85 

Argon  and  other  gases / 0.93 

Carbon  dioxide    ( average  > 0.03 

Total    ,,,...    100.00 

Properties  and  uses.  Nitrogen,  we  have  already 
learned,  is  extremely  inactive  and  does  not  combine 


122  A  YEAR  IN  SCIENCE 

readily  with  other  elements.  Because  it  is  so  inactive 
its  chief  function  in  relation  to  life  is  often  said  to  be 
"to  dilute  the  oxygen."  Since  nitrogen  constitutes 
more  than  three-fourths  of  the  weight  of  the  air,  the 
pressure  of  the  air,  the  force  of  the  wind,  the  flight  of 
birds  are  largely  possible  because  of  it. 

Another  important  use  of  nitrogen  is  as  a  plant  food. 
Most  plants  use  the  nitrogen  compounds  which  are  in 
the  soil.  These  in  solution  are  taken  into  the  plant 
through  its  roots.  When  plants  are  grown  in  the  same 
place  year  after  year,  they  take  out  so  much  of  the 
nitrogenous  matter  as  to  decrease  the  fertility  of  the 
soil.  If  the  soil  is  lacking  in  nitrogen,  no  plant  will 
thrive.  One  large  family  of  plants,  of  which  peas, 
beans,  alfalfa,  lentils,  and  a  number  of  others  are  men- 
bers,  have  on  their  roots  little  nodules  in  which  certain 
kinds  of  bacteria  live.  These  bacteria  possess  the 
power  of  absorbing  the  nitrogen  from  the  air  and  com- 
bining it  with  the  oxygen  and  some  of  the  salts  of  the 
earth  to  form  nitrates.  These  nitrates  are  very  valu- 
able as  plant  foods.  These  plants  are  now  extensively 
grown  not  only  for  their  value  as  crops,  but  also 
because  they  enrich  the  soil  by  adding  nitrogen  to  it. 

Oxygen  from  the  air  is  consumed  all  the  time  by  ani- 
mals and  plants  in  breathing.  Without  it  they  could 
not  live.  Oxygen,  we  have  already  learned,  combines 
readily  with  most  other  elements.  By  its  chemical 
union  with  other  elements  we  know  that  heat  and 
sometimes  light  are  produced.  This  heat,  developed  by 


ATMOSPHERE  123 

the  process  of  oxidation,  is  used  to  warm  houses,  to 
produce  steam,  to  run  trains,  to  drive  machinery,  and 
in  many  other  ways. 

The  readiness  with  which  oxygen  unites  with  most 
other  elements,  makes  it  an  important  agent  in  the  dis- 
integration of  rocks  and  minerals,  and  the  decomposi- 
tion of  dead  animal  and  plant  matter. 

In  spite  of  the  fact  that  oxygen  is  being  consumed 
all  the  time,  its  amount  does  not  appear  to  grow  less. 
Evidently  to  keep  this  equilibrium,  it  must  be  supplied 
as  fast  as  it  is  consumed.  This  is  true,  and  the  principal 
source  of  this  supply,  as  we  shall  see  later,  is  green 
plants. 

Carbon  dioxide,  though  present  only  in  small  amounts 
in  the  air,  is  extremely  important.  It  is  produced  con- 
stantly by  the  burning  of  fuel,  by  the  decay  of  organic 
matter,  and  by  animal  and  plant  respiration.  From 
these  various  sources  it  is  supplied  constantly  to  the 
atmosphere.  It  has  been  estimated  that  carbon  dioxide 
is  being  supplied  to  the  atmosphere  at  the  rate  of  about 
75  tons  per  second. 

Because  carbon  dioxide  is  formed  as  a  result  of  com- 
bustion and  respiration,  the  amount  of  it  in  the  air  in 
cities  is  greater  than  in  the  open  country. 

Carbon  dioxide  is  supplied  very  rapidly  to  the  air, 
yet  the  amount  of  it  remains  about  the  same.  We  infer, 
therefore,  that  in  some  way  this  gas  is  being  removed, 
or  taken  out  of  the  air,  about  as  rapidly  as  it  is  formed. 
Again  we  must  look  to  the  plant  for  the  explanation. 


124  A  YEAR  IN  SCIENCE 

Green  plants. use  the  carbon  dioxide  for  food,  and  in  so 
doing  they  remove  it  from  the  air. 

The  little  solid  particles  in  the  air  we  call  dust.  The 
amount  of  dust  in  the  atmosphere  is  always  great.  It 
is  constantly  settling  everywhere,  indoors  and  out, 
Avhenever  the  air  is  dry.  Much  of  the  dust  about  us 
is  harmless,  but  some  of  it  is  very  dangerous  because 
it  consists  of  minute  organisms  which  produce  diseases. 

Heat  is  received  by  the  air  from  several  sources,  but 
the  heat  from  the  sun  is  much  greater  than  that  from 
all  other  sources.  That  the  atmosphere  depends  chiefly 
upon  the  sun  for  its  heat  is  shown  by  the  variations  in 
temperature  from  day  to  night,  from  cloudy  days  to 
sunny  ones,  and  from  season  to  season. 

Moisture  in  atmosphere.  Water  vapor  is  supplied  by 
evaporation.  It  is  constantly  entering  the  atmosphere 
from  all  damp  surfaces  and  from  all  bodies  of  water.  Its 
presence  in  the  air  may  be  proved  in  various  ways.  If 
a  pitcher  of  ice  water  stands  in  a  warm  room,  drops  of 
water  appear  on  the  outside  of  it.  Window  panes  in  the 
winter  are  covered  with  moisture. 

The  amount  of  water  vapor  in  the  atmosphere  is* 
extremely  variable.  It  varies  from  place  to  place,  and 
from  time  to  time  in  the  same  place.  Some  water  vapor, 
however,  is  always  present,  even  in  the  desert  where  the 
air  seems  driest.  Since  we  can  not  see  nor  smell  this 
vapor  we  are  usually  not  conscious  of  its  presence. 

The  term  humidity  is  used  in  referring  to  the  amount 
of  moisture  in  the  air.  If  there  is  much  moisture,  we  say 


ATMOSPHERE  125 

that  the  humidity  is  high.  If  there  is  very  little,  we  say 
it  is  low.  When  there  is  as  much  water  vapor  in  the 
air  at  a  given  time  as  it  can  hold,  the  air  is  said  to  be 
saturated. 

Dew  point.  If  saturated  air  at  any  temperature  is 
cooled,  a  part  of  the  water  vapor  immediately  con- 
denses into  water.  When  water  vapor  is  condensed  in 
the  air  it  becomes  visible.  In  this  manner  dew,  frost, 
fog,  clouds,  rain,  and  snow  are  formed.  The  tempera- 
ture at  which  the  water  vapor  in  the  air  begins  to 
condense  is  called  the  dew  point. 

Dew  and  frost.  Due  to  radiation,  the  temperature  of 
the  surface  of  the  ground,  and  especially  of  the  vege- 
tation, becomes  lower  than  that  of  the  surrounding  air. 
This  occurs  frequently  in  the  clear  still  nights  of 
summer  and  autumn.  This  causes  the  invisible  water 
vapor  to  condense  as  dew.  We  thus  see  that  the  old 
saying  that  "dew  falls"  is  incorrect. 

Frost  is  formed  in  much  the  same  way  as  dew, 
although  in  this  case  the  formation  takes  place  below 
the  freezing  point  of  water.  The  water  vapor  then 
passes  directly  from  the  gaseous  state  to  the  solid 
state. 

Anything  which  will  check  the  cooling  of  the  ground 
and  the  lower  atmosphere  tends  to  prevent  the  forma- 
tion of  dew  and  frost.  A  cloudy  sky  prevents  excessive 
radiation.  Winds  constantly  change  the  air  and  thus 
hinder  cooling.  As  a  result,  it  is  rare  to  have  frost  on 
cloudy  or  windy  nights. 


126  A  YEAR  IN  SCIENCE 

Fog  and  clouds.  Fog  and  clouds  are  very  much  the 
same.  Fog  is  at  or  near  the  surface  of  the  earth,  while 
the  clouds  are  usually  half  a  mile  or  more  above  it.  In 
either  case,  a  warm  mass  of  air  carrying  large  quanti- 
ties of  water  vapor  is  cooled. 


Copyright  by  Henry   G.   Peabody. 
FIG.  45.  Sunrise  above  the  clouds,  Mt.  Washington,  New  Hampshire. 


Rain.  If  the  temperature  of  air  saturated  with  water 
vapor  is  greatly  lowered,  there  will  be  so  much  water 
condensed  that  it  will  collect  in  drops  which  are  too 
large  to  float.  Kain  then  takes  place,  and  continues  if 
the  condensation  continues. 

Snow  and  hail.  Snow  is  formed  in  the  same  way 
that  frost  is  formed.  It  forms  when  the  water  vapor 
passes  directly  into  the  solid  state.  Snow  crystals  are 
very  beautiful  and  are  of  many  varieties. 

Hail  is  frozen  rain.     The  rain  falls  through  a  layer 


ATMOSPHERE  127 

of  cold  air  and  is  frozen.  Frequently  the  small  hail 
stone  thus  formed  is  carried  about  by  currents  of  air 
and  more  layers  of  frozen  water  are  added  to  it.  This 
process  may  continue  for  some  time,  and  as  a  result  the 
large  hail  stones  with  which  we  are  all  familiar  are 
occasionally  formed.  Much  damage  to  windows  and 
crops  may  be  caused  by  the  larger  hail  stones. 


Questions 

1.  What  is  the  height  to  which  the  atmosphere 
extends  ? 

2.  What  is  meant  by  ' '  our  environment ' '  ? 

3.  Of  what  importance  is  atmosphere  to  us? 

4.  What     changes    may    take    place    in    the    at- 
mosphere ? 

5.  Is  air  a  mechanical  mixture  or  a  chemical  com- 
pound?    What  are  the  reasons  for  your  answer? 

6.  What  gases  are  found  in  the  air? 

7.  What  per  cent  of  each  of  these  gases  is  present  ? 

8.  Are    there    any    advantages    in    having    four- 
fifths   of  the   air   composed   of   an  inactive   gas   like 
nitrogen  ? 

9.  Explain  in  what  way  alfalfa  or   clover  makes 
soil  more  fertile. 

10.  Of  what  use  is  the  oxygen  in  the  air? 

11.  Why  does  not  the  supply  of  oxygen  become 
exhausted? 

12.  What  are  the  sources  of  carbon  dioxide  in  the 
air? 

13.  How    is    an    equilibrium    of    carbon    dioxide 
maintained? 


128  A  YEAR  IN  SCIENCE 

14.  Under  what  conditions  may  dust  be  harmful? 

15.  How  is  the  atmosphere  heated? 

16.  What  are.  the  sources   of  water  vapor  in  the 
atmosphere  ? 

17.  What    is    meant    by    the    expression    "air    is 
saturated"? 

18.  Define  humidity.     Dew  point. 

19.  Under  what  conditions  is  dew  formed?    Frost? 

20.  Why  does  covering  plants  with  a  piece  of  paper 
or  cloth  help  to  keep  them  from  freezing? 

21.  What  are  clouds?    What  is  their  distance  from 
the  surface  of  the  earth? 

22.  Under  what  conditions  is'  rain  formed?    Hail? 
Snow  ? 

23.  How  can  you  account  for  the  fact  that  a  large 
hailstone  is  made  of  concentric  layers  of  ice? 


CHAPTER  XIX 

ATMOSPHERIC  PRESSURE 

Introduction.  It  is  a  Avell  known  fact  that  water  has 
weight  and  exerts  pressure.  It  is  more  difficult  for  us 
to  believe  that  the  air  around  us  is  constantly  exerting 
pressure,  first,  because  we  do  not  feel  conscious  of  it; 
second,  because  air  is  invisible. 

Imagine  for  a  moment  that  extending  for  over  two 
hundred  miles  above  us  there  were  water.  We  can 
easily  appreciate  that  it  would  have  weight.  Similarly, 
the  air  above  us  has  weight,  and  hence  exerts  pressure. 
Suppose  we  consider  a  column  of  air  one  inch  wide  and 
one  inch  thick  and  over  two  hundred  miles  high.  If 
this  column  of  air  could  be  placed  upon  one  pan  of  a 
balance,  it  would  be  found  to  weigh  about  15  pounds. 
This  weight  would  vary  from  time  to  time,  and  from 
place  to  place.  If  we  weighed  the  column  of  air  extend- 
ing above  one  square  inch  on  top  of  a  mountain,  its 
weight  would  be  less  than  15  pounds,  because  the 
column  would  not  be  so  high. 

We  are  practically  never  conscious  of  this  really 
enormous  pressure  of  the  atmosphere,  which  is  exerted 
over  every  inch  of  qur  bodies.  We  are  not  conscious  of 
it  because  the  pressure  is  exerted  equally  over  the 

129 


130  A  YEAR  IN  SCIENCE 

inside  and  the  outside.  We  are  so  constructed  as  to  be 
most  healthy  when  under  this  pressure.  Without  it  we 
feel  uncomfortable.  If  this  pressure  is  suddenly 
changed  outside  of  our  bodies,  we  are  at  once  conscious 
of  it.  On  tops  of  high  mountains  breathing  becomes 
more  difficult,  headaches  and  other  results  follow. 

Aeronauts  have  never  ascended  much  higher  than 
seven  miles.  At  that  height  the  pressure,  outside  of 
the  body  is  reduced  to  about  one-fifth  of  what  it  is 
at  sea  level.  As  a  result  of  the  high  internal  pressure 
the  blood  is  forced  to  the  surface,  the  walls  of  the 
blood  vessels  frequently  rupture,  and  other  physical 
difficulties  result. 

Fish  living  at  the  bottom  of  the  sea  are  subjected  to 
enormous  pressure.  Nevertheless  they  are*  adapted  to 
those  great  depths.  Were  the  pressure  to  which  they 
are  accustomed  diminished  to  any  great  extent,  they 
Avould  suffer  great  pain,  and  possibly  death.  Alexander 
Agassiz  says:  "In  fish  brought  up  from  the  deep 
water,  the  swimming  bladder  often  protrudes  from  the 
mouth,  the  eyes  are  forced  out  of  their  sockets,  the 
scales  fall  off,  and  they  present  a  most  disreputable 
appearance." 

Just  as  they  are  adapted  to  the  pressure  at  the 
bottom  of  a  sea  of  water,  so  we  are  best  adapted  to 
the  pressure  near  the  bottom  of  a  sea  of  air. 

Air  presses  in  all  directions.  Place  a  piece  of  paste- 
board, or  blotting  paper,  over  the  mouth  of  a  tumbler 
filled  with  water.  Shake  the  tumbler  until  the  paper 


ATMOSPHERIC  PRESSURE 


131 


is   thoroughly   moistened.     Then  invert  the   tumbler. 
The  water  does  no.t  run  out  because  the  pressure  of  the 


A  B 

FIG.  46.  The  pasteboard  does  not  fall  off  from  the  tumbler 
because  the  pressure  of  the  air  on  the  outside  of  it  is  greater 
than  that  of  the  water  in  the  tumbler.  In  A}  the  air  presses  from 
below  ;  in  B,  from  the  side. 

air  outside  of  the  pasteboard  is  at  least  equal  to  the 
downward  pressure  of  the  water  in  the  tumbler. 

If  the  tumbler  is  held  so 
that  the  mouth  faces  side- 
wise,  the  water  does  not  run 
out,  because  the  air  also 
presses  upon  the  pasteboard 
from  the  sides. 

Tie  a  piece  of  sheet  rub- 
ber over  the  large  end  of  a 
bell  jar.  Now  exhaust  the 
air  from  the  belljar  by 
means  of  an  air  pump.  As  !Ma&  i\he  we'sht  °f 


FIG.    47.     when    air    is 

pumped  from   the   glass   jar, 


132  A  YEAR  IN  SCIENCE 

soon  as  a  part  of  the  air  is  pumped  out  of  the  glass,  the 
pressure  of  the  air  beneath  the  rubber  is  less  than  the 
pressure  of  the  air  above  it,  and  the  rubber  is  forced 
doAvn  into  the  glass. 

If  a  piece  of  glass  tubing  is  placed  in  a  beaker  of 
water,  the  water  will  not  rise  in  the  tube.  If  the  air  is 
then  drawn  out  of  the  tube  by  the  mouth,  the  water  will 
rise  in  the  tube.  When  the  air  is  withdrawn  from  the 
tube  by  the  mouth,  the  pressure  within  the  tube  is 
reduced.  The  liquid  is  then  forced  up  the  tube  be- 
cause of  the  pressure  of  the  air  on  the  surface  of  the 
water  in  the  beaker.  This  is  what  happens  when  we 
take  soda  water  or  lemonade  through  a  straw. 

A  test  tube  filled  with  water  is  closed  by  the  thumb 
and  then  inverted  mouth  downward  into  a  jar  of  water. 
After  the  thumb  is  removed  the  water  does  not  run 
out  of  the  test  tube,  because  the  pressure  of  the  air 
on  the  surface  of  the  water  is  sufficient  to  prevent  this. 

If  there  is  a  limit  to  the  amount  of  pressure  which 
the  air  exerts,  there  must  be  a  limit  to  the  column  of 
water  which  it  will  hold  up. 

If,  instead  of  a  short  test  tube,  a  tube  35  feet  or  more 
in  length  had  been  used,  would  the  result  have  been  the 
same  as  that  obtained  with  the  test  tube?  This  has 
been  tried.  Careful  experiments  have  shown  that  the 
pressure  of  the  air  at  sea  level  is  sufficient  to  hold  up 
about  34  feet  of  water. 

If  the  area  of  the  opening  at  the  base  of  the  tube 
is  one  square  inch  and  the  height  of  the  column  of 


ATMOSPHERIC  PRESSURE 


133 


water  is  34  feet,  it  has  been  determined  that  the  weight 
of  the  water  in  that  tube  is  14.7  pounds.  The  water 
is  therefore  pressing  downward  with  a  pressure  of  14.7 
pounds  to  the  square  inch.  The  air  is  pressing  down- 
ward on  the  surface  of  the  water  with  the  same  force. 
Column  of  mercury  held  by  air  pressure.  If  the 
water  were  twice  as  heavy  as  it  is,  the  column  of  water 
which  the  air  would  hold  up  would  be  only  about  17 
feet.  Mercury  is  13.6  times  as  heavy  as  water,  conse- 
quently the  highest  column  of  mercury  which  can  be 
held  up  by  atmospheric  pressure  is  1/13.6  of  34  feet. 


of  about  2.5  feet,  or  30  inches. 

This  can  easily  be  demon- 
strated. Fill  a  glass  tube,  a  Tor- 
ricellian tube,  about  36  inches 
long,  with  mercury.  Close  the 
open  end  of  the  tube  with  the 
finger  and  then  quickly  insert  the 
end  of  the  inverted  tube  into  a 
dish  of  mercury.  When  the  finger 
is  removed,  the  mercury  falls 
somewhat.  If  the  height  of  the 
mercury  is  measured,  it  will  be 
found  to  be  about  30  inches, 
exactly  what  we  should  expect. 
If  tubes  of  very  different  diam- 
eters are  taken,  it  will  be  found 
that  mercury  can  be  held  up  to 
the  same  vertical  height  in  all  of 


30  in. 


Mercury 


Water 


FIG.  48.  Air  sup- 
ports a  column  of 
mercury  30  inches, 
a  column  of  water 
34  feet. 


134 


A  YEAR  IN  SCIENCE 


the  tubes.  The  shortness  of  the  mercury  tube  compared 
with  that  of  water  makes  the  use  of  mercury  more 
convenient  for  both  experimental  and  practical  pur- 
poses. 

Variations  in  pressure  due  to  elevation.  The  pressure 
of  the  atmosphere  upon  any  square  inch  of  surface 
depends  upon  the  total  quantity  of  air  directly  over- 
lying that  surface.  The  quantity  will  be  greater  at 
the  level  of  the  sea  than  on  the  summit  of  a  high 
mountain,  in  the  bottom  of  a  valley  than  on  top  of  a 
hill,  at  the  base  of  a  building  than  in  one  of  its  upper 
stories. 

Other  factors  determine  the  pressure  as  well  as  ele- 
vation. Condition  of  the  weather,  temperature,  winds, 
amount  of  water  vapor,  all  tend  to  modify  the  atmos- 
pheric pressure  not  only  from  day  to  day,  but  even 
from  hour  to  hour.  It  is  possible  to  record  these 
changes  in  pressure.  The  instrument 
used  for  this  is  called  a  barometer. 

Barometer.  A  glass  tube  with 
thick  walls,  closed  at  one  end,  is 
filled  with  mercury.  This  is  then 
inverted  into  a  small  dish  of  mer- 
cury. The  whole  is  attached  to  a 
board  which  is  marked  in  inches  or 
centimeters.  As  the  pressure  of  air 
upon  the  surface  of  the  mercury  in 
the  dish  varies,  the  level  of  the  liquid 
Fia  bl™m£te£imple  ^  the  tube  rises  or  falls. 


ATMOSPHERIC  PRESSURE 


135 


Use  of  the  barometer.  The  barom- 
eter may  be  used  to  determine  eleva- 
tions. At  sea  level  the  barometer  will 
read  30  inches.  If  the  barometer  be 
carried  to  elevations  above  sea  level, 
the  mercury  gradually  falls.  It  falls 
at  the  rate  of  one  inch  for  a  rise  in 
elevation  of  about  910  feet. 

Changes  in  air  pressure  are  also  very 
closely  connected  with  changes  in  the 
weather.  In  general  it  may  be  said 
that  a  rapid  rise  of  the  mercury  in  the 
barometer  indicates  fair  weather,  and 
a  rapid  fall  indicates  stormy  weather. 
The  barometer  is  thus  of  great  assist- 
ance in  predicting  the  general  trend 
of  the  weather. 

Questions 

1.  How  can  you  prove  that  air  has 
weight  ? 

2.  What  is  the  weight  of  a  column 
of   air   over    one    square    inch    at    sea 
level? 

3.  Why    is    not    the    atmospheric 
pressure  on  the  top  of  a  mountain  the 
same  as  it  is  at  the  bottom? 

4. 
scious  of  the  great  pressure  of  the  air  around  us? 

5.     What  are  some  of  the  effects  of  high  altitudes 
on  the  human  body? 


FIG.  50.  A 
standard  mer- 
curial barom- 

Why   are   we   not   always   con-    eter- 


136  A  YEAR  IN  SCIENCE 

6.  How  high  will  the  atmosphere  hold  a  column 
of  water?    Of  mercury?    How  do  you  account  for  the 
difference  in  these  heights? 

7.  Does  the  height  of  the  column  of  mercury  held 
by  the  atmosphere  vary  with  the  diameter  of  the  tube  ? 

8.  How    can   you   prove    that    air    presses    in   all 
directions  ? 

9.  Does  the  pressure  of  the  atmosphere  vary?     If 
so,  under  what  conditions? 

10.  What  is  the  structure  of  a  barometer? 

11.  Why  do  we  use  mercury  in  a  barometer  instead 
of  some  other  liquids? 

12.  What  are  the  uses  of  a  barometer? 

13.  What  kind  of  weather  does  a  high  barometer 
indicate?    A  low  one? 


CHAPTER  XX 

WINDS  AND  STORMS 

Winds.  We  are  all  familiar  with  the  sometimes 
regular,  but  more  often  fitful  and  irregular  movements 
of  the  air,  which  we  call  winds. 

Winds  are  important  in  many  ways.  They  transfer 
great  masses  of  air  from  one  part  of  the  earth  to  an- 
other ;  they  carry  away  the  impurities  of  city  air ;  they 
furnish  power  for  windmills  and  sailing  vessels ;  they 
cool  hot  regions  and  warm  cold  ones.  Most  changes 
of  weather  are  due  to  changes  in  the  direction  of  the 
wind.  Some  winds  are  agree- 
able and  favorable  to  life. 
Some  bring  suffering,  de- 
struction, and  death.  Even 
light  breezes  effect  a  con- 
tinual change  of  air  which  is 
beneficial  for  both  plants  and 
animals.  To  man,  winds  are 
as  a  rule  stimulating  and 
invigorating,  while  calm  air 
is  often  enervating. 

Cause  of  winds.  A  piece 
of  wire  gauze  is  placed  over 
the  flame  of  a  Bunsen  burner. 
If  very  small  pieces  of  cotton  are  dropped  upon  the 

137 


P 


_<fr. 


FIG.  51.  When  air  is 
heated  it  expands,  becomes 
lighter,  and  is  pushed  up  by 
the  colder  air  which  is 
drawn  down  beneath  it. 


138  A  YEAR  IN  SCIENCE 


they  soon  rise,  being  carried  upward  by  the  cur- 
rents of  heated  air* 

We  already  know  that  when  air  is  heated  it  expands 
and  becomes  lighter.  The  surrounding  colder  air, 
because  it  is  heavier,  is  then  forced  into  the  place  occu- 
pied by  the  heated  lighter  air.  The  heated  air  is  then 
pushed  up  and  produces  an  air  current.  This,  on  a 
small  scale,  is  a  wind.  If  for  any  reason  the  air  above 
one  place  becomes  heavier  than  that  above  another, 
there  will  be  a  transfer  of  air  from  the  place  where  the 
pressure  is  greater  to  that  where  it  is  less.  This  move- 
ment of  the  air  we  call  wind.  Winds  are  caused  by 
unequal  pressure.  The  inequality  of  pressure  is  usually 
the  result  of  unequal  heating. 

It  is  a  well  known  fact  that  all  parts  of  the  earth 
are  not  equally  heated.  It  is  also  known  that  the 
amount  of  heat  received  by  the  earth  at  any  given 
place  varies  from  hour  to  hour,  day  to  night,  and 
month  to  month.  These  variations  in  temperature  are 
largely  the  result  of  the  shape  of  the  earth,  its  move- 
ments, and  its  position  with  reference  to  the  sun. 

Just  as  the  earth  is  unequally  heated,  so  likewise  is 
the  air  immediately  above  it  unequally  heated.  As  a 
result  the  pressure  of  the  air  varies  in  different  places, 
being  lightest  where  the  air  is  hottest,  and  heaviest 
where  its  temperature  is  lowest.  In  those  portions 
where  the  earth  is  greatly  heated,  the  warm  air  will  be 
pushed  up  by  the  cold  air  from  the  surrounding  regions 
which  will  come  in  to  fill  its  place. 


WINDS  AND  STORMS 


139 


General  effect  of  unequal  heating*.  The  effect  of 
heating  the  earth  is  to  cause  the  air  to  rise  from  the 
surface.  Since  all  parts  of  the  earth  are  not  evenly 
heated,  the  air  does  not  rise  evenly.  It  rises  most 
over  the  equator  and  in  the  tropics  where  the  earth 
receives  the  greatest  amount  of  heat.  This  warm 
upper  air  moves  from  equatorial  regions  toward  the 
poles.  As  it  does  so,  it  gradually  becomes  cooler 
and  consequently  heavier,  until  in  the  regions  of  30 
degrees  north  and 
south  of  the  equator, 
it  settles  down  upon 
the  earth.  This  move-  °t 
ment  of  the  air  estab- 
lishes a  region  of 
high  pressure  in  each 
hemisphere.  From 
each  of  these  regions  ^ 
currents  of  air  move 
outward ;  one  toward 
the  nearest  pole,  and 
one  toward  the  equa- 
tor. The  elements  of 
the  general  circula-  poles> 
tion,  then,  are :  1.  the  rising  of  warm  air  in  the  tropics, 
2.  the  moving  poleward  of  this  air,  3.  its  settling,  4.  the 
moving  poleward  of  part  of  this  air  and  the  moving 
equatorward  of  the  remainder. 

If  the  earth  did  not  rotate,  the  poleward  moving 


FIG.  52.  Diagram  of  the  general 
circulation  '  of  the  air.  The  trade 
winds  blow  toward  the  equator,  the 
prevailing  westerlies  blow  toward  the 


14()  A  YEAR  IX  SCIENCE 

air  would  move  north  in  the  northern  hemisphere  and 
south  in  the  southern  hemisphere.  The  air  moving 
toward  the  equator  would  move  directly  south  in 
the  northern  hemisphere  and  north  in  the  southern. 
The  rotation  of  the  earth,  however,  turns  the  currents 
of  air  to  the  right  in  the  northern  hemisphere  and  to 
the  left  in  the  southern.  (See  Figure  52.)  Thus  in  the 
temperate  regions  of  both  hemispheres,  the  winds 
usually  come  from  the  west.  These  winds  are  known 
as  the  prevailing  westerlies.  The  winds  blowing  from 
the  regions  of  high  pressure  toward  the  equator  are 
known  as  the  trade  winds.  They  blow  obliquely  toward 
the  equator  from  the  northeast  and  from  the  south- 
east. These  winds  have  been  given  their  name  on 
account  of  the  steadiness  with  which  they  blow.  Navi- 
gators have-  known  of  these  wrinds  and  have  taken 
advantage  of  them  for  ages. 

The  prevailing  westerlies  are  of  the  most  importance 
and  of  the  most  interest  to  us  because  the  United 
States  lies  in  their  region.  Because  of  the  regularity 
of  these  winds  most  of  our  storms  move  eastward. 
We  are  all  familiar  with  the  fact  that  our  storms  are 
generally  first  seen  in  'the  west. 

Land  and  sea  breezes.  If  you  have  lived  near  a 
large  body  of  water,  you  are  familiar  with  the  cool 
breezes  which  blow  from  the  water  over  the  land 
during  the  day,  and  in  the  opposite  direction  at  night. 
Land  heats  and  also  cools  more  rapidly  than  water. 
As  a  result,  during  a  hot  day  the  land  becomes  warmer 


WINDS  AND  STORMS 


141 


than  an  adjacent  body  of  water.  The  air  above  the 
land  also  becomes  Avarmer  and  expands  more  than 
that  over  the  water.  This  expansion  reduces  the  pres- 
sure and  causes  the  air  to  move  toward  the  land  from 
the  water.  This  movement  of  the  air  is  of  great  value 
along  denseh-  populated  sea  coasts  or  lakes.  This  sea 
breeze,  as  it  is  called,  lowers  the  temperature  and  also 
brings  in  pure  air. 

At  night  the  land  cools  more  rapidly  than  the  water. 
Consequently  breezes  bloAv  from  the  land  to  the  water. 

Cyclones.  The  regularity  of  the  general  system  of 
prevailing  winds  is  frequently  disturbed  by  local  and 
temporary  disturbances  which  are  called  storms.  These 
are  brought  about 
by  the  fact  that  the 
atmospheric  pressure  N 
is  not  the  same  in  all 
places  at  the  same 
time.  For  example, 
if  we  should  receive 
reports  of  baromet-  s 
ric  readings  from  a 
number  of  places  in 
the  United  States 
taken  at  the  same 
time,  we  should  find 
that  they  were  not  all  alike.  In  some  parts  of  the  coun- 
try the  readings  would  be  high,  in  other  parts  low.  As 
a  result  of  the  differences  in  pressure,  there  is  always 


FIG.  53.  Diagram  to  show  the  cir- 
culation of  air  about  a  low  and  about  a 
high.  The  rotation  of  the  earth  turns 
the  currents  9f  air  to  the  right  in  the 
northern  hemisphere  and  to  the  left  in 
the  southern  hemisphere. 


142  A  YEAR  IN  SCIENCE 

a  movement  of  air  from  the  region  of  high  pressure 
toward  the  one  of  low.  Such  a  movement  is  called  a 
cyclone.  We  must  not  think  that  a  cyclone  is  always 
a  violent,  destructive  wind  storm.  Such  storms  are 
correctly  known  as  tornadoes. 

At  the  same  time  that  there  is  a  movement  in  toward 
a  region  of  low  pressure,  there  is  also  an  outward 
movement  from  the  area  of  high  pressure.  Such  a 
movement  is  known  as  an  anticyclone. 

Because  of  the  rotation  of  the  earth,  cyclonic  winds 
do  not  blow  straight  toward  the  center  of  the  region 
of  low  pressure.  In.  the  northern  hemisphere  they 
are  deflected  toward  the  right.  (See  Figure  53.) 

A  region  of  low  pressure  is  generally  characterized 
by  rain,  relatively  high  temperature,  and  shifting 
winds.  These  conditions  constitute  a  cyclonic  storm. 
A  cyclone  is  not  stationary,  but  moves  generally  in  an 
eastward  or  north  eastward  direction.  As  it  moves 
it  is  followed  by  an  area  of  high  pressure  in  which 
the  winds  are  moving  spirally  out  from  the  center. 
This  anticyclone  is  associated  with  low  temperature 
and  clear  skies.  Frequently  during  a  cyclone  so  much 
warm  air  from  the  south  is  brought  into  northern 
regions  that  unseasonable  warm  weather  follows. 
Similarly,  sometimes  cold  air  spreads  over  a  great  area 
extending  south.  When  accompanied  by  a  driving 
snowr  this  constitutes  a  blizzard. 

Thunderstorms.  We  are  all  familiar  with  the  char- 
acteristic conditions  of  the  atmosphere  and  sky  pre- 


WINDS  AND  STORMS  '143 

ceding  and  during  thunderstorms.  This  type  of  storm 
is  frequent  in  the  United  States.  It  occurs  in  cyclones, 
but  usually  some  distance  from  the  center  and  toward 
the  south. 

A  thunderstorm  generally  occurs  in  the  warm  season 
and  often  follows  a  period  of  intense  heat.  The  first 
indication  of  a  thunderstorm  in  temperate  latitudes  is 
a  large  dark  cloud  in  the  west.  It  moves  eastward, 
preceded  by  a  sharp  breeze.  The  sky  becomes  over- 
spread and  rain  pours  down.  The  rainfall  is  often 
heavy  and  the  drops  are  large.  It  lasts,  however,  but 
a  short  time,  usually  less  than  an  hour.  The  sky  then 
becomes  clear,  and  the  air  is  noticeably-  cooler  and 
fresher. 

Frequently  in  a  thunderstorm  the  sun  appears  when 
some  rain  is  still  falling.  A  rainbow  may  then  be 
seen  opposite  the  sun.  As  the  sun's  rays  pass  through 
the  drops  of  water,  the  white  light  of  which  the  ray 
is  composed  is  broken  up  into  a  number  of  different 
colored  rays. 

The  lightning  which  accompanies  a  thunderstorm  is 
due  to  the  fact  that  electricity  is  produced  when  water 
condenses  rapidly  in  the  air.  Each  drop  of  water 
becomes  charged  with  electricity,  which  is  then  dis- 
charged between  clouds,  between  parts  of  clouds,  or 
between  the  earth  and  the  clouds. 

The  flashes  of  lightning  cause  vibrations  in  the  air 

•  which  produce  a  noise,  which  w~e  call  thunder.    Sound 

travels  much  more  slowly  than  light ;  consequently  we 


144  A  YEAR  IN  SCIENCE 

hear  the  thunder  some  time  after  we  have  seen  the 
lightning. 

Tornadoes.  Like  thunderstorms,  tornadoes  occur  in 
hot  weather  and  generally  in  a  cyclone.  They  differ 
from  a  cyclone  because  the  atmospheric  pressure  at 
the  center  is  very  low,  and  the  area  of  low  pressure 
is  very  small.  In  some  tornadoes  the  atmospheric 
pressure  has  been  reduced  as  much  as  one-half.  As 
a  result,  the  winds  are  violent  and  very  destructive. 
It  is  probable  that  in  some  instances  the  velocity  of 
the  wind  is  as  great  as  500  miles  an  hour.  Fortu- 
nately tornadoes  do  not  occur  frequently,  and  the  path 
over  which  they  travel  is  very  narrow.  In  tornadoes 
of  recent  years  in  the  United  States  many  lives  have 
been  lost  and  much  property  destroyed.  In  St.  Louis 
in  1896  the  property  loss  was  estimated  at  $13,000,000, 
and  in  Louisville  in  1890  at  $2,500,000.  Tornadoes  at 
sea  are  called  water  spouts. 

Effect  of  winds  on  rainfall.  We  can  scarcely  over- 
estimate the  importance  of  rainfall  to  all  living  things. 
We  know  that  much  of  our  own  western  country  has 
remained  uninhabited  because  the  annual  rainfall  is 
not  sufficient  to  enable  plants  to  grow,  or  because 
it  does  not  fall  during  the  growing  period  of  plants. 
We  do  not  have  any  extensive  deserts  in  the  United 
States,  yet  about  one-third  of  the  land  is  too  arid  to 
grow  crops  successfully.  By  means  of  irrigation  we 
are  succeeding  in  watering  artificially  millions  oft 
acres  of  land.  Because  of  the  fertility  of  the  soil  and 


\VIXDS  AND  STORMS 

the  abundant  sunshine,  luxuriant  crops  can  then  be 
grown  in  these  otherwise  arid  regions. 

Winds  are  important  factors  in  the  distribution  of 
the  rainfall.  Air  becomes  filled  with  moisture  over 
surfaces  where  water  is  evaporating.  This  moisture 
laden  air  is  carried  along  until  it  comes  to  a  region 
of  lower  temperature  or  higher  pressure,  where  the 
vapor  condenses  and  falls  as  rain. 


Photograph  by  Henry  G.  Peabody. 
FIG.   54.      Columbia   River  Valley  in  Washington. 
The  ranches  on  this  plain  are  irrigated  by  streams  which  come 
down  from   the  mountains  in  the  distance.      The  land  in  the  fore- 
ground has  not  been  reclaimed  and  is  covered  with  sagebrush. 


Since  the  prevailing  winds«in  the  United  States  are 
for  the  -  most  part  from  the  southwest,  those  which 
blow  toward  the  land  along  the  western  coast  are 
filled  with  moisture  from  the  Pacific  Ocean.  In  the 
summer  the  land  is  warmer  than  the  ocean,  and  the 
winds  blowing  over  the  lowlands  along  the  coast  do 
not  deposit  their  moisture  until  they  reach  the  nioun- 


146  A  YEAR  IN  SCIENCE 

tains.  This  causes  the  dry  summer  season  character- 
istic of  much  of  California.  Along  the  coast  of  Wash- 
ington the  mountains  are  very  close  to  the  coast  line, 
and  moisture  is  deposited  where  the  winds  strike  the 
high  mountains.  Washington,  as  ,a  result,  does  not 
have  the  dry  summer  season  characteristic  of  the 
southern  part  of  the  western  coast. 

In  the  winter  the  land  is  cooler  than  the  ocean; 
consequently  the  winds  begin  to  give  up-  their  mois- 
ture as  they  blow  over  the  lowlands,  and  continue  to 
do  so  until  they  reach  the  Cascades  in  the  north  and 
Sierras  in  the  south.  Beyond  the  mountains  the  air  is 
then  dry.  The  winds  descend  and  blow  over  the  low- 
lands and  form  the  arid  lands  of  the  Great  Basin, 
eastern  Oregon,  and  Washington.  As  the  winds  con- 
tinue eastward  they  strike  the  Eocky  Mountains  where 
they  are  again  cooled  and  their  moisture  is  deposited. 
East  of  the  Rocky  Mountains  as  far  as  the  Atlantic 
these  winds  are  dry,  for  they  do  not  cross  any  more 
high  mountains  and  the  temperature  is  not  low  enough 
to  cause"  precipitation.  East  of  central  Kansas  and 
Nebraska  the  lands  are  well  supplied  with  rain.  This 
rainfall  is  not  due  to  the  prevailing  westerlies,  how- 
ever, but  to  cyclonic  storms. 

The  amount  of  rainfall  in  the  United  States  varies 
from  over  60  inches  per  year  along  the  coast  of 
Washington  and  Oregon  and  part  of  Florida,  to  less 
than  5  inches  in  parts  of  Nevada,  southern  California, 
Arizona,  and  Utah. 


WINDS  AND  STORMS  147 

Questions 

1.  State    three    ways    in    which    winds    are     of 
importance. 

2.  What  is  the  principal  cause  of  winds? 

3.  What  is  the  direction  of  the  movement  of  air 
over  the  equator  and  in  the  tropics? 

4.  In  what  latitude  does  this  air  begin  to  settle 
down  on  the  surface  of  the  earth? 

5.  In  what  directions  does  the  air  move  from  the 
regions  of  high  pressure  formed  at  30°  north  and  south 
latitudes  ? 

6.  Why   do   not    prevailing   winds   blow   directly 
north  and  south? 

7.  Toward  what  direction  are  winds  deflected  in 
the  northern  hemisphere?     In  the  southern? 

8.  What  are  the  prevailing  westerlies? 

9.  What  are  the  trade  winds? 

10.  What  are  land  and  sea  breezes  ?    What  causes 
them? 

11.  What  are  the  characteristics  of  a  cyclone  ?    An 
anticyclone  ? 

12.  Under  what  conditions  do  thunderstorms  arise? 

13.  What  is  the  cause  of  a  rainbow  ? 

14.  How  do  you  account  for  lightning?     Thunder? 

15.  Why  do^sr.e  hear  thunder  some  time  after  we 
have  seen  the  lightning? 

16.  How  could  we  estimate  the  distance  from  the 
earth  to  the  clouds  during  a  thunderstorm? 

17.  What  is  a  blizzard? 

18.  Why  are  tornadoes  so  destructive? 

19.  In  what  parts  of  the  United  States  have  we  had 
tornadoes? 

20.  What  is  a  water  spout? 


148  A  YEAR  IN  SCIENCE 

21.  Of  what  importance  is  rainfall  to  man? 

22.  What  is  meant  by  irrigation? 

23.  What  proportion   of  the   land   in   the   United 
States  is  too  arid  to  grow  crops  successfully? 

24.  How  can  you  account  for  the  wet  and  dry  sea- 
sons of  Southern  California? 

25.  Why  is  there  a  scanty  rainfall  just  east  of  the 
Eocky  Mountains? 

26.  What  is  the  average  rainfall  in  the  region  in 
which  you  live? 

27.  What  is  the  cause  of  most  of  the  rain  in  the 
Middle  West? 

28.  In  what  parts  of  the  United  States  is  the  amount 
of  rainfall  greatest? 

29.  What  parts  have  the  least  rain? 


CHAPTER  XXI 
WEATHER  AND  CLIMATE 

Weather.  The  condition  of  the  atmosphere  at  any 
given  time  constitutes  the  weather.  The  amount  of 
rain,  the  atmospheric  pressure,  the  direction  and  the 
velocity  of  the  wind,  the  humidity,  the  state  of  the 
sky,  and  the  temperature  are  factors  which  determine 
the  kind  of  weather.  We  are  well  aware  of  the  fact 
that  one  of  the  most  prominent  characteristics  of  the 
weather  is  its  changeableiiess.  The  variations  in  tho 
weather  are  brought  about  by  the  rotation  of  the 
earth  on  its  own  axis,  its  inclination  011  its  axis,  its 
revolution  around  the  sun,  and  such  changes  as  result 
from  the  passage  of  storms. 

Climate.  When  we  speak  of  the  climate  of  any 
region  we  say  it  is  cold,  hot,  temperate,  dry,  or  wet. 
We  are  then  referring  to  the  average  weather  condi- 
tions of  that  region  for  a  long  period  of  time.  In 
general  the  weather  of  any  region  follows  the  same 
course  from  year  to  year.  Occasionally,  however,  a 
winter  may  be  very  mild,  or  there  may  be  an  un- 
usually heavy  snow.  It  is  thus  necessary  to  have  the 
average  of  the  weather  conditions  for  a  long  period 

149 


150  A  YEAR  IN  SCIENCE 

of  years  in  order  to  determine  the  climate  of  that 
region. 

There  is  a  popular  notion,  especially  among  old  peo- 
ple, that  the  climate  of  the  region  in  which  they  are 
living  is  changing.  Records  of  the  climate  extending 
over  long  periods  of  time  indicate  that  there  is  little 
basis  for  this  current  impression.  A  few  exceptional 
seasons,  an  intensely  cold  winter  or  a  very  wet  sum- 
mer, make  a  greater  impression  and  are  consequently 
the  ones  which  are  best  remembered. 

The  principal  elements  of  climate  are  moisture, 
wind,  and  temperature.  In  previous  chapters  we  have 
discussed  the  general  distribution  of  wind  and  rainfall. 


FIG.  55.  The  amount  of  heat  received  depends  upon  the  angle 
at  which  the  sun's  rays  strike  the  surface  of  the  earth.  The  same 
number  of  rays  fall  on  a  smaller  area  at  A  than  at  B. 

Effect  of  temperature  on  climate.  Practically  all 
the  heat  which  warms  our  atmosphere  comes  from 
the  sun.  This  is  shown  by  the  difference  in  tempera- 
ture between  day  and  night,  and  between  that  on  a 


WEATHER  AXD  CLIMATE  151 

cloudy  and  a  sunny  day.  The  sun's  rays  falling  all 
day  on  the  land  and  water  warm  them.  This  heat 
then  radiates  outward  and  heats  the  air,  which  receives 
very  little  heat  directly. 

The  surface  of  the  earth  receives  most  heat  where 
the  sun's  rays  fall  most  nearly  vertically.  The  rays 
are  then  most  concentrated  and  pass  through  less  air. 
We  are  all  familiar  with  the  fact  that  the  air  is 

Noon 


FIG.  56.  Diagrani  showing  the  difference  in  the  angles  at  which 
the  sun's  rays  strike  the  earth  at  sunrise,  noon,  and  sunset. 

warmer  at  noon  when  the  sun's  rays  are  nearly  verti- 
cal than  it  is  in  the  evening  or  in  the  morning  when 
they  are  oblique. 

Day  and  night.  In  your  study  of  geography  you 
learned  that  the  earth  rotates  on  its  own  axis  once  in 
twenty-four  hours,  and  also  that  it  revolves  about  the 
sun  in  a  little  more  than  three  hundred  and  sixty- 
five  days.  As  a  result  of  the  rotation. of  the  earth  on 
its  own  axis,  any  given  point  on  the  earth  is  turned 
during  part  of  each  twenty-four  hours  toward  the 
sun,  producing  day,  and  during  the  remainder  of  the 
time  away  from  the  sun,  producing  night.  The  uni- 
form succession  of  days  and  nights  is  due  to  the  regu- 
laritv  of  the  rotation  of  the  earth. 


152  A  YEAR  IN  SCIENCE 

Seasons.  Seasonal  changes  in  temperature  are  the 
result  of  the  revolution  of  the  earth  about  the  sun. 
The  path  of  the  earth  about  the  sun  is  known  as  its 
orbit.  This  orbit  is  an  ellipse ;  consequently  the  dis- 
tance from  the  sun  to  the  earth  varies  from  time  to 
time.  As  the  earth  moves,  its  axis  (a  line  drawn 
through  the  center  of  the  earth  from  pole  to  pole)  is 
not  perpendicular  to  the  plane  of  its  orbit.  It"  is 
inclined  toward  this  plane  at  an  angle  of  about  23Vi> 
degrees.  This  position  of  the  axis,  together  with  the 
motion  of  the  earth,  causes  the  changes  in  the  length 
of  day  and  night  and  also  the  succession  of  seasons. 

One  half  of  the  earth  is  being  illuminated  by  the 
sun's  rays  all  of  the  time.  If  the  earth's  axis  were 
perpendicular  to  the  plane  of  its  orbit,  day  and  night 
would  ahvays  be  of  equal  length.  Since  the  rays  of 
light  wrould  then  always  fall  at  the  same  angle  and 
for  the  same  length  of  time  at  a  given  place  on  the 
earth,  there  would  be  no  change  of  season. 

We  all  know,  however,  that  in  June  the  sun  shines 

more  directly  on  the  earth  in  the  temperate  latitude, 

• 

and  also  for  several  hours  more  than  it  does  in  Jan- 
uary. As  a  result,  the  temperature  of  several  months 
which  we  call  summer,  is  higher  than  that  of  winter. 
In  autumn  and  spring  the  angle  of  the  rays  and  the 
length  of  daytime  are  intermediate. 

By  referring  to  Figure  57  you  will  notice  that  the 
hemispheres  are  at  one  time  inclined  toward  the  sun 
and  at  another  away  from  it.  For  example,  from 


WEATHER  AND  CLIMATE  153 

March  21  to  September  22  the  northern  hemisphere 
is  inclined  toward  the  sun.  During  that  time  the 
region  around  the  north  pole  receives  light  contin- 


June  21 


FIG.  57.  Diagram  of  the  path  of  the  earth  around  the  sun 
showing  the  position  of  the  earth  with  reference  to  the  sun  on 
four  dates.  The  dotted  line  represents  an  ellipse,  and  the  earth 
and  sun  are  in  the  same  plane. 

uously  for  some  time.  Throughout  all  the  northern 
hemisphere,  during  this  period,  the  days  are  longer 
than  the  nights. 

The  rays  are  most  nearly  vertical  in  our  latitude 
on  June  21,  and  our  day  is  then  the  longest  and  our 
night  the  shortest.  From  then  on,  the  inclination  of 
the  earth's  axis  toward  the  sun  becomes  less  until 
September  22,  when  it  is  at  right  angles  to  the  sun 
and  the  day  and  night  are  equal  in  length. 

Gradually  the  north  pole  becomes  inclined  away 
from  the  sun,  the  rays  from  the  sun  become  more  and 
more  oblique  in  the  northern  hemisphere,  the  tempera- 
ture becomes  lower,  and  the  nights  become  longer. 


154  A  YEAR  IN  SCIENCE 

On  December  21  we  have  our  shortest  day.  The  days 
then  gradually  become  longer  until  on  March  21  the 
nights  and  days  are  again  equal. 

The  hottest  days  in  our  latitude  do  not  come  in  June 
at  the  time  when  the  sun's  rays  are  most  nearly  vertical. 
During  the  long  days  at  that  time  more  heat  is  received 
by  the  earth  than  is  given  off  during  the  short  nights. 
There  is  thus  a  gradual  accumulation  of  heat,  and  our 
hottest  days  come  later  in  the  summer.  During  the  fall 
the  earth  slowly  loses  more  heat  than  it  receives,  but  it 
is  some  time  after  our  shortest  day,  December  21,  that  we 
have  our  coldest  weather. 

The  change  of  seasons  and  the  difference  in  the  length 
of  day  and  night  vary  greatly  with  the  latitude.  In  the 
temperate  regions  there  are  four  seasons,  summer,  fall, 
winter,  and  spring.  In  the  polar  regions  the  difference 
is  chiefly  a  matter  of  daylight  and  of  darkness.  Seasons 
differ  but  little  in  the  tropics  because  the  days  and  the 
nights  are  always  nearly  equal,  and  the  sun's  rays  are 
nearly  vertical  all  the  time. 

All  the  variations  which  are  due  to  day  and  night, 
seasons,  rainfall,  winds,  etc.,  are  of  great  importance 
to  the  life  of  man  and  to  human  industries.  The  dis- 
tribution of  life  is  largely  the  result  of  climate. 

Weather  maps.  Weather  maps  are  prepared  every 
day  by  the  United  States  Weather  Bureau,  which  is  a 
part  of  the  Department  of  Agriculture.  Telegrams 
are  received  daily  at  the  Weather  Bureau  from  sta- 
tions in  different  parts  of  the  country.  Each  telegram 


WEATHER  AND  CLIMATE  155 

tells  the  temperature,  direction  and  velocity  of  the 
wind,  pressure,  rainfall  or  snowfall,  cloudiness,  etc., 
at  the  station  from  which  the  report  is  sent. 

These  reports  are  then  combined  and  placed  upon 
a  map.  From  these  maps  it  is  then  possible  for  an 
expert  to  tell  not  only  what  the  weather  is,  but  also 
to  predict  what  it  is  likely  to  be.  These  predictions 
are  sometimes  wrong,  due  to  the  fact  that  reports 
from  some  stations  may  be  missing  or  to  a  change  in 
the  rate  at  which  a  storm  is  advancing.  The  few  mis- 
takes made,  however,  are  almost  negligible  as  com- 
pared with  the  many  correct  forecasts. 

Through  the  services  of  the  Weather  Bureau  warn- 
ings of  coming  frosts,  storms,  and  floods  are  made 
which  save  annually  not  only  many  lives,  but  millions 
of  dollars'  worth  of  property.  Millions  of  dollars' 
worth  of  fruit  may  be  saved  by  these  warnings  of  cold 
waves  sent  to  fruit  growers.  Shipping  interests  are 
also  .served  by  warnings  of  approaching  storms. 

Explanation  of  a  weather  map.  If  we  examine  a 
weather  map  (see  Figure  58),  we  notice  that  there 
are  many  things  represented  on  it.  Let  us  give  our 
attention  first  to  the  heavy  black  lines.  These  lines 
are  isobars  (iso,  equal;  barus,  heavy).  All  the  weather 
stations  on  the  map  which  have  the  same  barometric 
pressure  are  joined  by  a  solid  line.  At  the  end  of 
each  of  these  lines  is  marked  the  figure  which  repre- 
sents the  pressure  at  all  points  on  the  line.  These 
lines  make  it  possible  to  see  very  easily  where  the  high 


156 


A  YEAR  IN  SCIENCE 


WEATHER  AND  CLIMATE 


157 


158  A  YEAR  IN  SCIENCE 

and  low  pressure  centers  are  located.  The  isobars 
curve  in  irregular  circular  lines  about  these  areas  of 
high  and  low  pressures.  We  have  already  learned 
that  low  centers  are  those  toward  which  air  tends  to 
move  from  all  sides.  This  movement  toward  a  low 
pressure  area  constitutes  a  cyclone.  Consequently  a 
low  pressure  represents  a  storm  center.  A  high  .pres- 
sure on  the  other  hand,  represents  an  anticyclone,  or 
a  region  of  fair  clear  weather.  By  examining  weather 
maps  of  several  successive  days  it  is  possible  to  trace 
the  path  of  a  low  area  as  it  moves  along  and  across 
the  country.  (See  Figures  58  and  59.)  The  path  of 
the  high  pressure  area  which  follows  it  can  also  be 
traced.  Arrows  on  the  map  indicate  the  direction  of 
the  winds.  Places  of  equal  temperature  are  also  indi- 
cated on  a  weather  map.  They  are  connected  by 
dotted  lines  which  are  called  isotherms. 


Questions 

1.  What  are  the  principal  causes  of  variations  in 
the  weather? 

2.  Explain    the    differences    between    the    terms 
weather  and  climate. 

3.  Explain  the   causes   of  the   differences   in  the 
seasons. 

4.  How  do  you  account  for  the  fact  that  cloudy 
days  are  cooler  than  days  on  which  the  sun  is  shining? 

5.  Why  is  it  warmer  at  noon  than  it  is  in  the  morn- 
ing or  evening? 


WEATHER  AXD  CLIMATE  159 

6.  What  causes  day  and  night? 

7.  Why  do  day  and  night  vary  in  length? 

8.  How  many  degrees   is  the   inclination   of  the 
earth's  axis  to  the  plane  of  its  orbit? 

9.  What  is  the  position  of  the  earth  with  reference 
to  the  sun  on  June  21?    September  22?    December  21 
and  March  21? 

10.  Has  climate  in  any  way  affected  the  distribution 
of  man  ? 

11.  How  are  weather  maps  made? 

12.  Of  what  value  are  weather  maps? 

13.  What  are  isobars?    Isotherms? 

14.  Are  weather  forecasts  generally  correct  ? 

15.  Why  is  it  sometimes  difficult  to  make  accurate 
weather  predictions  ? 

16.  Of  what  value  are  weather  forecasts? 

17.  Is    the    government    justified    in    maintaining 
weather  bureaus? 

18.  Where  is  the  weather  station  located  which  is 
nearest  to  the  place  in  which  you  are  living? 


CHAPTER  XXII 

THE  SURFACE  OF  THE  EARTH 

Everybody  has  observed  that  the  surface  of  the 
earth  is  not  smooth,  but  more  or  less  irregular.  Some 
of  these  irregularities,  as  mountains  and  large  valleys, 
are  very  conspicuous,  while  others,  as  hills,  ravines, 
ridges,  cliffs,  and  flats,  are  less  conspicuous,  but  more 
widely  distributed.  These  irregularities,  which  make 
up  the  relief  features  of  the  earth,  may  be  classified  as 
follows :  continents  and  oceans ;  mountains,  plateaus, 
and  plains;  and  minor  land  forms. 

Continents  and  oceans.  The  relief  features  of  the 
first  group,  the  continents  and  ocean  basins,  have  prac- 
tically always  occupied  the  positions  they  now  have. 
It  is  not  positively  known  how  they  came  to  originate 
or  to  occupy  these  positions.  When  the  earth  cooled 
from  its  original  heated  condition,  there  was  a  down 
folding  where  the  ocean  beds  now  are,  and  a  corres- 
ponding elevation  over  the  continental  areas.  When 
the  surface  of  the  earth  was  cool  enough  to  allow  the 
atmospheric  waters  to  remain,  they  accumulated  in 
the  depressions,  and  thus  made  the  seas. 

Although  in  name  there  are  five  great  oceans,  in 
reality  there  is  but  one.  As  all  the  ocean  water  of  the 

160 


THE  SURFACE  OF  THE  EARTH         161 

earth  is  one  continuous  body,  it  is  only  for  convenience 
that  different  parts  have  received  different  names. 
In  area  the  ocean  covers  about  three-fourths  of  the 
earth's  surface.  Its  average  depth  is  about  two  and 
one-half  miles.  If  all  irregularities  of  the  earth's 
crust  were  smoothed  off,  the  water  would  cover  the 
entire  earth's  surface  to  a  depth  of  nearly  9,000  feet. 
The  ocean  is  continually  at  war  with  the  land.  Its 
main  work,  with  the  aid  of  rain  and  streams,  is  to 
carry  the  land  into  the  sea.  Charlotte  P.  Stetson  has 
expressed  it  thus : 

I  am  the  Sea !    I  hold  the  land 
As  one  holds  an  apple  in  his  hand; 
Hold  it  fast  with  sleepless. eyes, 
Watching  the  continents  sink  and  rise. 
Out  of  my  bosom  the  mountains  grow, 
Back  to  its  depths  they  crumble  slow. 
The  iron  cliffs  that  edge  the  land 
I  grind  to  pebbles  and  sift  to  sand; 
I  comfort  the  earth  with  rains  and  snows 
Till  waves  the  harvest  and  laughs  the  rose. 
Flower  and  forest  and  child  of  breath 
With  me  have  life — without  me  death. 
The  earth  is  a  helpless  child  to  me. 
I  am'  the  sea ! 

The  ocean  may  never  entirely  complete  its  task. 
Water  is  held  on  the  surface  of  the  earth  by  the  inter- 
ior heat  which  allows  it  to  penetrate  only  to  a  certain 


162  A  YEAR  IN  SCIENCE 

depth.  As  the  heat  recedes  towards  the  center  of  the 
earth  by  cooling,  the  waters  follow.  In  the  very 
remote  future  the  earth  will  have  cooled  to  a  depth 
permitting  the  absorption  of  all  the  water  and  atmo- 
sphere now  on  its  surface.  Such  is  considered  to  be 
the  condition  of  the  moon  now. 

Continents  are  great  bodies  of  land  surrounded  by 
water.  The  average  height  of  the  land  above  sea  is 
less  than  one-half  mile.  While  continents  have  under- 
gone many  changes  in  the  past,  they  have  practically 
always  occupied  their  present  position. 

Mountains,  plateaus,  and  plains.  Mountains,  the 
glory  of  the  earth,  the  culminating  places  of  scenic 
grandeur  and  beauty,  are  the  most  conspicuous  land 
forms.  Most  mountain  systems  are  located  on  the 
sides  of  continents  adjacent  to  the  ocean ;  furthermore, 
the  highest  mountains  border  the  largest  oceans.  The 
birthplaces  of  mountains  are  marginal  sea  bottoms. 
As  the  interior  of  the  earth  loses  heat  it  contracts. 
But,  as  the  crust  of  the  earth  is  already  cool,  it  is 
more  or  less  rigid ;  hence,  to  accommodate  itself  to 
the  shrinking  interior,  it  must  fold.  This  folding 
naturally  takes  place  along  lines  of  weakness  in  the 
earth's  crust.  Marginal  sea  bottoms  are  lines  of  weak- 
ness. Here  for  ages  have  accumulated  enormous 
deposits  of  sediment.  As  the  sediment  accumulates, 
the  interior  heat  rises  toward  the  surface,  and  in  the 
presence  of  water  included  in  the  sediment,  produces, 
a  semi-fused  condition,  This  condition,  of  course,  pro-. 


THE  SURFACE  OF  THE  EARTH 


163 


duces  lines  of  weakness  where  folding  will  occur.  This 
process  goes  on  very  slowly.  To  produce  mountains 
like  the  Rockies  has  taken  untold  ages  of  time.  In 
every  mountain  there  is  a  period  of  birth,  growth, 
maturity,  decay,  and  death.  The  Appalachian  moun- 
tains are  now  in  the  period  of  decay ;  at  one  time  they 
were  almost  as  high  as  the  Rockies. 


Permission  of  U.  S.   Geological  Survey. 
FIG.   60.     An  anticlinal  fold  in  the  rock  at  Levis  Terrane,  Quebec. 

Plateaus  are  highlands  of  considerable  area.  Not  all 
plateaus  are  the  same  height;  the  Piedmont  Plateau 
between  the  Appalachian  Mountains  and  the  Atlantic 
Ocean  is  rather  low;  while  the  Plateau  of  Tibet  is 
about  15,000  feet  high. 

Plains  are  the  lowlands  of  the  earth.  They  have 
great  economic  importance,  for  here  is  located  $ 


164  A  YEAR  IN  SCIENCE 

large  part  of  the  agricultural  lands.  They  differ 
greatly  in  height,  origin,  fertility,  position,  and  shape 
of  surface.  Plateaus  and  plains,  like  mountains,  fre- 
quently have  their  origin  in  the  folding  of  the  earth's 
crust. 

Minor  land  forms.  Hills,  cliffs,  mesas,  buttes,  ridges, 
flats,  and  other  minor  land  forms  constitute  the  third 
group  of  relief  features.  They,  unlike  the  other 
groups,  are  caused  by  erosion  and  weathering  brought 
about  by  the  atmosphere  and  water. 

Effect  of  the  atmosphere  on  the  earth's  surface.  The 
atmosphere  has  both  a  mechanical  and  a  chemical 
effect  upon  the  earth's  surface. 

Mechanical.  Small  particles  can  be  blown  about 
from  place  to  place  by  the  wind.  This  is  a  mechanical 
change.  Dust  is  the  easiest  material  for  the  wind  to 
move.  The  sources  of  dust  are  highways,  fields, 
streets,  volcanoes,  meteoric  smoke,  pollen,  and  spores 
of  plants.  During  some  volcanic  eruptions  much  dust 
is  thrown  into  the  air  and  carried  long  distances  by 
the  wind.  Meteors  or  "shooting  stars"  when  they 
come  into  the  atmosphere  from  outer  space  are  prob- 
ably traveling  eighteen  or  twenty  miles  per  second. 
The  friction  of  the  atmosphere  is  sufficient  to  heat 
them  to  such  a  temperature  that  they  are  consumed. 
The  dust  resulting  settles  to  the  earth.  It  is  said  that 
the  bottom  of  the  deep  sea  is  covered  to  a  considerable 
depth  with  this  meteoric  dust  free  from  other  accumu- 
lations. Loess  beds  are  deposits  of  dust  which  occur 


THE  SURFACE  OF  THE  EARTH 


165 


at  different  places.  In  the  Province  of  Shansi,  China, 
are  deposits  several  hundred  feet  thick.  •  Near  Kan- 
sas City,  Missouri,  there  is  a  deposit  at  least  thirty 
feet  thick. 

Sand  is  also  carried  by  the  wind,  but  since  it  is 
heavier  than  dust,  a 
much  stronger  wind 
is  necessary  for  car- 
rying it.  Sand  never 
rises  to  any  great 
height,  but  is  carried 
near  the  earth.  There 
are  many  obstacles 
on  the  earth  to  stop 
it.  Sand  blown  by  a 
strong  Avind  has  con- 
siderable cutting 
force.  For  this  rea- 
son sand  blasts  are  sometimes  used  for  etching  glass. 
In  the  semi-arid  regions  of  western  United  States,  pro- 
jecting rock  cliffs  are  often  carved  into  strange  and 
fantastic  forms.  The  softer  parts  of  the  rock  are  cut 
more  rapidly  so  that  the  harder  parts  are  left  project- 
ing. Even  the  hard  rocks  are  not  able  to  withstand 
the  long  continued  action  of  blown  sand. 

Sand  dunes.  Mounds  and  ridges  of  wind-blown  sand 
are  called  dunes.  In  the  dry  parts  of  western  United 
States  there  are  thousands  of  square  miles  where 
dunes  are  abundant.  On  the  east  and  south  shores  of 


Photograph    by  Detroit  Publishing   Co. 

FIG.  61.  Balanced  Rock,  Colorado 
Springs,  Colorado.  This  rock  has  been 
yut  by  wind-blown  sand. 


166 


A  YEAR  IN  SCIENCE 


CopyrigJit  "by  Underwood  &   Underwood,  N.  Y. 

FIG.   62.     A  forest  on   Cape  Cod   planted  as  a  windbreak   is   being 
buried    by     drifting-    sand. 

Lake  Michigan  are  other  sand  dune  regions.  Dunes 
vary  much  in  size.  Very  large  ones  occur  in  central 
Wyoming.  The  largest  ones  are  found  in  the  Sahara 
Desert  where  they  reach  a  height  of  several  hundred 
feet. 

The  growth  of  a  dune  begins  when  the  sand  is 
stopped  by  some  object  on  the  earth's  surface.  Once 
started,  the  dune  increases  by  the  addition  of  more 


THE  SURFACE  OF  THE  EARTH        167 

sand.  They  are  not  stationary,  but  migrate  in  the 
direction  toward  which  the  prevailing  wind  blows. 
The  migration  of  the  dunes  may  do  great  damage  by 
covering  up  farm  land,  forests,  railroads,  and  some- 


FIG.   63.     The  pines  and  grasses  shown  at  the  left  hold   the  sand 
and  prevent  the  migration  of  the  sand  dune. 


times  buildings.  Trees,  shrubs,  and  grasses  that  will 
grow  in  sand  are  sometimes  planted  on  dunes  to  pre- 
vent their  migration.  The  roots  of  the  plants  hold 
the  sand. 

Effect  of  change  of  temperature  on  rocks.  Changes 
in  the  temperature  of  the  atmosphere  also  have  a 
mechanical  effect  on  the  earth's  surface.  You  have 
already  learned  that  heat  expands  and  cold  contracts 
objects.  Exposed  rock  surfaces  are  heated  in  the  day 
and  cooled  at  night.  On  mountain  tops  this  daily 
change  of  temperature  is  very  great.  This  continual 


168  A  YEAR  IN  SCIENCE 

change  of  temperature  causes  rocks  to  scale  off.  In 
mountainous  regions  great  piles  of  this  broken  off 
debris  collect  at  the  base  of  mountains  and  cliffs.  Such 
deposits  are  called  talus.  The  total  effect  of  this  shell- 


Permission  of  U.  8.   Geological  Survey. 

FIG.   64.     Great  piles  of  debris,  called  talus,  have  collected  at  the 
base   of   these  mountain   peaks    in   Colorado. 

ing  off  of  exposed  rock  surfaces  through  the  ages  has 
been  very  great.  If  you  examine  the  surface  of  a 
boulder  or  rock,  you  can  notice  this  shelling  off  effect. 
Chemical.  The  oxygen  of  the  air  is  its  most  active 
chemical  element.  If  a  piece  of  iron  is  exposed  to 
the  air  in  the  presence  of  moisture,  it  rusts.  The 
oxygen  of  the  air  unites  with  the  iron  and  forms  a 
red  rust;  in  time  the  whole  of  the  iron  is  converted 
into  the  oxide.  Oxygen  attacks  many  rocks  in  a  simi- 
lar manner.  As  the  oxidizing  process  is  continually 
going  on,  the  total  effect  is  very  considerable.  Other 


THE  SURFACE  OF  THE  EARTH 


169 


constituents  of  the  air  may  also  attack  rocks  chemi- 
cally, but  oxygen  is  the  most  powerful. 

Work  of  rain  in  causing1  relief.    All  have  observed 
that  streams  are  muddy  after  a  heavy  rainfall.     This 


PIG.    65. 


Permission  of    United   States   Forest  Service. 
Gullies  in  a  hillside   formed  by   running  water. 


muddiness  is  caused  by  the  rain  carrying  soil  into 
the  streams.  With  every  rain  more  or  less  earth  is 
discharged  into  streams;  the  total  effect  of  rain  ero- 
sion is  enormous.  Perhaps  rain  has  had  more  to  do 
with  producing  relief  features  than  any  other  one 
agent.  Its  effect  as  an  erosive  agent  is  more  notice- 


170  A  YEAR  IN  SCIENCE 

able  in  hilly  and  mountainous  regions.  The  gullies 
and  ravines  cut  in  hillsides  attest  this  fact.  The  fan- 
like  deposits  of  soil  often  seen  at  the  end  of  these  gul- 
lies and  ravines  also  give  evidence  of  the  power  of 
rain  in  moving  soil  and  earth.  It  has  been  estimated 
that  the  Mississippi  Valley  is  lowered  one  foot  every 
5,000  years  by  this  erosion.  As  the  Mississippi  Valley 
is  considered  to  be  an  average  one,  this  may  be  con- 
sidered to  be  the  average  rate  of  erosion  of  the  earth's 
surface.  Add  to  this  the  solvent  effect  of  rain  water 
on  the  soil,  and  the  total  lowering  is  about  one  foot  in 
4,000  years.  This  impresses  us  with  the  fact  that  the 
continents  are  indeed  on  their  way  to  the  sea.  Tenny- 
son in  his  "In  Memoriam"  has  written: 

The  hills  are  shadows  and  they  flow 
From  form  to  form,  and  nothing  stands : 
They  melt  like  mist,  the  solid  lands, 
Like  clouds,  they  shape  themselves  and  go. 


Questions 

1.  Name  and  locate  on  a  map  of  the  world  the  five 
great  oceans. 

2.  What  proportion  of  the  area  of  the  earth's  sur- 
face do  these  oceans  cover?     What  is  their  average 
depth? 

3.  Name  and  locate  the  continents. 

4.  Do    mountain,    systems    border    oceans?      Give 
examples  to  illustrate  your  answer. 


THE  SURFACE  OF  THE  EARTH         171 

5.  Name  and  locate  the  principal  mountain  sys- 
tems in  the  United  States. 

6.  What  change  takes  place  in  the  earth's  crust 
to  form  mountains? 

7.  Which   are   older,   the  Rocky   or  Appalachian 
Mountains  ?    How  do  they  differ  ? 

8.  Name    the    principal    industries    in    mountain 
regions. 

9.  What  is  a  plateau? 

10.  Of  what  economic  importance  are  the  plains  of 
the  United  States? 

11.  What  are  the  principal  sources  of  dust  ? 

12.  If  sand  is  blown  by  a  strong  wind,  what  are  some 
of  the  effects  which  it  has  on  the  earth 's  surface  ? 

13.  How  are  sand  dunes  formed?     Why  are  they 
destructive  to  plant  life?    How  can  their  migration  be 
prevented  ? 

14.  Explain  how  rocks  are  broken  off  by  changes 
in  the  temperature  of  the  atmosphere. 

15.  Where  is  this  effect  most  evident? 

16.  How  is  the  earth's  surface  changed  as  a  result 
of  the  chemical  action  of  the  atmosphere? 

17.  What  is  meant  by  erosion? 

18.  Explain     fully     why     erosion     is     of     great 
importance. 


CHAPTER  XXIII 
STREAMS  AND  THEIR  WORK 

Introduction.  Rain  that  falls  on  the  earth  is  dis- 
posed of  in  three  different  ways :  part  may  evaporate ; 
part  may  immediately  run  off  into  streams ;  part 
may  sink  into  the  ground.  Of  that  which  sinks  into 
the  ground  a  portion  may  gradually  rise  to  the  sur- 
face by  capillary  action  and  then  evaporate ;  another 
portion  may  come  to  the  surface  as  springs;  still 
another  portion  may  never  appear  again  on  the  sur- 
face, but  may  find  its  way  to  the  sea  by  underground 
passage. 

Streams  and  stream  erosion.  Streams  receive  their 
water  from  several  sources :  rainfall,  lakes,  ponds,  and 
melting  snow  and  ice  from  mountain  tops,  as  well  as 
ground  water. 

We  are  all  aware  of  the  fact  that  streams  carry 
sediment ;  in  fact,  it  frequently  appears  that  the  princi- 
pal work  of  a  stream  is  to  carry  land  into  the  sea. 
All  streams  are  incessantly  at  this  task  of  lowering 
their  valleys  to  the  lowest  possible  level.  We  can  thus 
understand  why  streams  are  important  factors  in  modi- 
fying the  topography  of  the  land. 

The  erosive  power  of  a  stream  depends  upon  four' 

172 


STREAMS  AND  THEIR  WORK  173 

conditions:  first,  the  swiftness  of  the  current;  sec- 
ond, the  volume  of  the  water;  third,  the  amount  of 
sediment  it  carries;  fourth,  the  character  of  the  sur- 
faco  oyr-r  which  it  flows.  At  flood  time  the  erosive 


Permission  of  U.  S.  Geological  Survey. 

FIG.  66.  Alluvial  fan  at  the  mouth  of  Aztec  Gulch,  south- 
western Colorado.  The  deposit  at  the  base  of  this  slope  is  left 
by  the  running  water  when  its  velocity  is  suddenly  checked. 


power  of  a  stream  is  greatest,  for  then  it  floAvs  with 
greater  velocity,  as  it  has  a  larger  volume  of  water. 
As  a  result,  we  find  it  carries  much  more  sediment  then 
than  at  any  other  time.  This  sediment  in  turn  makes 
it  possible  for  the  stream  to  have  a  great  erosive  effect. 
By  being  rolled  along  the  bed  and  against  the  banks, 
the  sediment  scours  the  bed  deeper  and  broader.  The 
carrying  power  of  a  stream  varies  as  the  sixth  power 
of  the  velocitv.  If  the  velocitv  is  doubled  at  flood 


174 


A  YEAR  IN  SCIENCE 


time,  it  can  carry  stones  sixty-four  times  as  heavy  as 
at  the  normal  stage,  for  2x2x2x2x2x2  =  64.  Thus  as 
the  velocity  of  some  mountain  streams  is  increased 
many  times  during  floods,  we  may  easily  account  for 


Copyright  7020  T)y  Perry  Pictures  Co. 
FIG.    67.      Arroyo    Seco   River,    Sierra   Madre   Mountains,    Southern 

California. 

Stones   serve   as   tools   for  cutting  river  beds   deeper   and  broader. 
In   this   process   the   stones   become    smooth   and   rounded. 


the   marvelous   power   that   these   streams   exhibit   in 
transporting  enormous  boulders   great  distances. 

The  amount  of  sediment  carried  by  streams  is  enorm- 
ous. It  is  calculated  that  the  Mississippi  River  carries 
more  than  1,000,000  tons  of  rich  soil  into  the  Gulf  of 
Mexico  every  day.  The  yearly  loss  to  the  country  of 
this  soil  is  said  to  be  about  $500,000,000.  As  this  is  a 
very  serious  loss,  and  in  some  parts  of  the  country  soil 


STREAMS  A>s'D  THEIR  WORK  175 

erosion  is  more  rapid  tkan  soil  formation,  the  problem 
of  lessening  soil  erosion  is  one  of  the  important  tasks 
of  conservation.  It  takes  about  10,000  years  to  form 
one  foot  of  residual  soil;  that  is,  soil  that  remains  in 
the  place  where  it  is  formed.  The  methods  generally 
employed  to  prevent  soil  erosion  are:  first,  deep  cul- 
tivation of  the  soil  allows  the  water  to  penetrate  the 
soil  and  not  to  run  off  and  carry  the  soil  with  it. 
Second,  in  hilly  countries,  plowing  at  right  angles  to 
the  slope  instead  of  up  and  down  the  slope  saves  the 
soil.  The  furrows  check  and  hold  most  of  the  sedi- 
ment. Third,  covering  the  soil  with  vegetation,  as 
growing  crops,  prevents  erosion.  Fourth,  growing 
grasses  on  the  slopes  tends  to  hold  the  soil.  Fifth, 
planting  forests  on  the  steep  slopes  checks  soil  move- 
ment. Sixth,  the  building  of  terraces  makes  a  series 
of  level  plains.  This  problem  of  soil  conservation  is 
an  important  one  and  should  receive  consideration  by 
every  land  owner. 

Stream  development.  A  stream  goes  through  three 
stages  of  development :  youth,  maturity,  and  old  age. 
These  terms,  as  related  to  streams,  do  not  refer  to 
years  but  rather  to  stages  of  development.  Each 
stage  has  features  that  are  characteristically  its  own. 
A  river  in  youth  has  some  or  all  of  the  following  char- 
acteristics : 

First,  a  young  river  bed  has  a  steep  slope.  Enough 
time  has  not  elapsed  so  that  the  stream  has  eroded 
its  bed  to  a  gentle  slope. 


176 


A  YEAR  IN  SCIENCE 


Second,  it  has  a  rapid  current.    The  velocity  of  flow 
is  largely  determined  by  the  steepness  of  the  slope. 

Third,  its  course 
is  comparatively 
straight.  When  a 
stream  originates, 
the  drainage  runs 
along  the  lowest 
level  of  the 
ground,  which  is 
usually  a  straight 
course.  Streams 
have  a  tendency 
to  become  more 
and  more  crooked 
as  they  g  r  o  w 
older. 

Fourth,  young 
streams  have  nar- 
row and  V-shaped 
valleys.  The  first 
work  a  stream  has 
to  do  is  to  erode 
its  bed  to  a  low  level ;  after  the  most  of  the  downward 
erosion  has  been  accomplished  it  begins  eroding  the 
sides.  A  V-shaped  valley  indicates  very  little  lateral 
erosion;  hence,  it  may  be  concluded  that  the  stream  is 
young.  •* 

Fifth,  there  is  practically  no  flood-plain.     By  this 


FIG.    68.      A   gorge   cut   by   the    Colorado 

River.      A    young    river    valley    is 

narrow,    its    sides    are    steep,    and 

the  stream  forming  it  is  swift. 


STREAMS  AXD  THEIR  WORK 


177 


term  is  meant  the  low  lalid  along  a  stream  that  is 
flooded  in  time  of  high  water.  A  flood-plain  is  formed 
by  the  stream  widening  its  valley  by  erosion  on  the 
sides.  If  the  stream  has  not  lowered  its  bed  to  the 
level  where  lateral  erosion  can  take  place,  it  is  in  a 
stage  of  youth. 


FIG.    69.      Waterfall   in   Catskill   Mountains,   New   York. 

Sixth,  waterfalls  are  frequent  along -the  courses  of 
young  streams.  To  produce  a  waterfall  there  must 
be  a  hard  stratum  of  rock  over  which  the  stream  is 


178  A  YEAR  IN  SCIENCE 

flowing;  under  this  is  a  softer  stratum.  At  Niagara 
Falls  there  is  a  solid  compact  layer  of  limestone  at  the 
top  with  softer  shale  underneath.  The  water  falling 
over  the  falls  wears  away  the  soft  shale.  As  this  con- 
tinues the  limestone  is  left  projecting ;  finally,  this 
limestone  breaks  off  and  falls  into  the  stream  below. 
Thus  the  falls  slowly  recede  up  stream.  At  Niagara 
the  rate  of  recession  .is  about  five  feet  per  year.  Falls 
may  disappear  from  stream  courses:  first,  by  the 
recession  of  the  falls  to  the  source  of  the  stream;  sec- 
ond, by  bed  erosion,  entirely  removing  the  hard  strata. 
Then  the  falls  may  become  rapids  and  finally  disap- 
pear. Long  periods  of  time  are  required  to  accomplish 
either  of  these  results. 

Seventh,  lakes  in  the  course  of  a  stream  indicate  a 
period  of  youth.  Streams  are  the  enemies  of  lakes, 
and  in  two  ways  are  Working  for  their  destruction. 
First,  the  outlet  is  being  lowered  by  erosion.  The 
level  of  the  lake  falls  as  erosion  of  the  outlet  pro- 
ceeds. Second,  the  stream  flowing  into  the  lake  brings 
sediment  wrhich  is  deposited  in  the  lake,  and  thus  fills 
it.  Both  of  these  forces  at  work  finally  cause  the  dis- 
appearance of  the  lake. 

The  Yellowstone,  Upper  Colorado,  Snake,  Green,  and 
Grand  Rivers  are  the  best  examples  of  young  streams 
in  this  country. 

Maturity.  A  mature  stream  has  the  following  char- 
acteristics: first,  the  slope  is  rather  gentle,  as  erosion 
has  accomplished  this;  second,  the  current  is  not  very 


STREAMS  AND  THEIR  WORK 


179 


swift ;  third,  its  flood  plain  has  been  formed  by  lateral 
erosion ;  fourth,  its  course  is  rather  crooked,  and  winds 
back  and  forth  across  the  flood  plain ;  fifth,  its  valley 
is  wide  and  its  sides  are  not  steep,  the  V-shaped  val- 


Photoyraph  by  Detroit  Publishing  Company. 
FIG.  70.     A  river  in  maturity. 


ley  of  the  young  stream  having  disappeared  by  erosion ; 
sixth,  waterfalls  are  few,  for  most  of  them  have 
been  destroyed  by  erosion ;  seventh,  unless  the  lakes 
were  very  large,  erosion  and  sedimentation  have  caused 
them  to  disappear ;  eighth,  a  mature  stream  carries  a 
moderate  amount  of  sediment.  The  Middle  Mississippi, 
the  Ohio,  and  the  Wabash  Rivers  show  the  result  of 
these  conditions. 

Old  age.    In  an  old  stream  we  find  the  influence  of 
erosion  still  more  marked: 


180  A  YEAR  IN  SCIENCE 

First,  its  bed  has  a  very  gentle  slope.  It  has  been 
eroded  to  base  level,  the  lowest  level  to  which  a  stream 
can  erode  its  bed  and  still  leave  slope  enough  for  the 
flow  of  water.  Very  few  if  any  streams  have  reached 
this  condition  throughout  their  entire  course. 

Second,  it  has  wide  flood-plains.  As  this  erosion 
in  the  bed  is  nearly  finished,  most  of  the  erosion 
is  on  the  sides.  As  a  result  of  this  action  in  some 
places  the  flood-plain  of  the  lower  Mississippi  River  is 
eighty  miles  wide.  The  most  fertile  land  is  found 
on  flood-plains  of  rivers.  Perhaps  the  most  famous 
flood-plain  of  any  river  is  that  of  the  Nile,  which  for 
almost  7,000  years  has  supported  a  dense  population. 
The  floodTplains  of  the  Euphrates  and  Tigris  are  almost 
equally  as  famous,  as  it  is  thought  the  birth  of  civili- 
zation, occurred  on  the  flood-plains  of  these  rivers. 
The  most  extensive  flood-plains  in  the  world  are  those 
of  the  Ganges  in  India  and  the  Hoang-Ho  in  China. 

Third,  an  old  river  is  very  crooked.  It  meanders 
to  and  fro  across  the  flood-plain,  because  the  soft  places 
have  eroded  more  rapidly  than  the  harder,  and  as  a 
result  there  are  hollows  in  the  bank.  .The  current  is 
deflected  by  the  hollow  across  to  the  opposite  side  where 
it  cuts  into  the  side.  This  deflection  of  the  current  back 
and  forth  across  the  stream  finally,  produces  a  very 
winding  course. 

Fourth,  the  valley  of  an  old  stream  is  wide,  with 
very  gentle  slopes. 


STREAMS  AND  THEIR  WORK  181 

Fifth,  waterfalls,  rapids,  and  lakes  have  been  elimi- 
nated from  the  course  of  old  streams  by  erosion. 

Study  the  streams  of  your  vicinity  to  determine  to 
what  stage  of  development  they  belong.  As  you  travel 
from  one  part  of  the  country  to  another  study  the 
streams  in  a  similar  manner. 

Accidents  to  stream  development.  Streams  meet 
with  many  accidents  during  their  life  history.  Few 
streams,  if  any,  go  through  theirv  entire  development 
uninterrupted.  Among  the  important  accidents  that 
may  happen  to  stream  development  are : 

First,  the  rising  of  the  land.  If  the  land  rises  just  as 
rapidly  as  the  downward  erosion  of  the  stream,  it  will 
remain  at  a  constant  stage  of  development.  If  the 
land  rises  faster  than  the  downward  cutting,  the  slope 
will  become  steeper  and  the  current  will  be  accel- 
erated. Such  a  stream  is  said  to  be  rejuvenated,  as  it 
is  taking  on  the  characteristics  of  youth. 

Second,  the  subsidence  of  the  land.  If  the  land  is 
subsiding,  the  slope  becomes  less  steep  and  the  current 
slower.  Erosion  in  the  bed  is  lessened  but  erosion  of 
the  banks  is  increased.  If  the  subsidence  is  below  base 
level,  the  stream  will  deposit  sediment  in  its  bed  in 
an  attempt  to  build  the  bed  up  to  base  level.  When 
the  subsidence  of  the  land  is  below  base  level,  water 
from  the  ocean  or  lake  will  flow  up  the  stream  and 
cover  the  valley,  and  in  this  way  form  a  drowned 
river  valley.  Many  rivers  of  the  New  England  States, 


A  YEAR  IN  SCIENCE 

as  well  as  the  Hudson,  the  Delaware,  the  St.  Law- 
rence, the  Susquehanna,  and  the  Potomac  Rivers  have 
drowned  valleys.  Some  of  the  finest  harbors  in  the 
world  are  drowned  river  valleys. 

Third,  the  migration  of  the  divide.  A  divide  is  a 
ridge  or  mountain  chain  dividing  two  river  systems. 
If  erosion  on  one  side  of  the  divide  is  more  rapid  than 
on  the  other,  the  divide  will  migrate  in  the  direction 
of  the  least  erosion.  This  may  cause  the  streams  on 
that  side  of  the  divide  to  disappear. 

Fourth,  glaciers.  Glaciers  sometimes  make  deposits 
across  stream  valleys,  causing  the  formation  of  lakes  or 
necessitating  the  stream's  taking  another  course. 

Streams  as  factors  in  human  activities.  From  the 
beginning  of  history  people  have  chosen  to  live  near 
streams,  probably  because  they  found  in  them  a  means 
not  only  for  producing  food,  but  also  for  conveying 
themselves  to  other  sections  of  the  country.  We  find 
in  the  early  history  of  the  United  States  that  all  of 
the  settlements  were  made  on  the  coast  and,  com- 
monly, near  the  mouth  of  a  river.  As  the  people  trav- 
eled inland  the  navigable  streams  w^ere  the  centers  of 
greatest  population. 

The  most  of  these  navigable  streams  had  flood- 
plains  which  were,  from  time  to  time,  enriched  by  the 
layers  of  sediment  brought  down  in  the  water.  The 
loss  caused  by  destruction  of  property  during  these 
floods  is  usually  equalled  or  exceeded  by  the  benefit 
gained  from  the  fertile  layer  of  soil  that  is  deposited. 


STREAMS  AND  THEIR  WORK  133 

The  people  living  in  the  flood-plain  of  the  Nile  depend 
upon  the  deposits  made  by  the  river  during  its  annual 
overflow.  As  the  flood-plain  of  the  Mississippi  is 
enriched  in  a  similar  way,  it  is  important  as  an  agri- 
cultural region. 

Until  the  use  of  steam  and  electricity,  streams  were 
the  most  important  means  for  travel.  Even  now  the 
courses  of  rivers  are  followed  in  exploration  of  a  new 
country.  It  is  economical  to  transport  by  water  many 
materials  when  time  is  not  an  important  element,  as 
transportation  by  water  is  cheaper  than  by  railway. 
In  hilly  or  mountainous  regions  railroads  are  always 
built  along  the  water  courses. 

As  the  population  of  the  country  increases,  so  does 
the  demand  for  food;  this  necessitates  a  larger  area 
for  growing  crops.  Rivers  help  in  making  this  pos- 
sible, as  they  are  the  main  sources  for  irrigation  pur- 
poses. The  semi-arid  lands  of  western  United  States, 
where  not  enough  rain  falls  for  agricultural  purposes, 
are  irrigated.  The  Government  has  under  way  thirty 
projects  which  will  irrigate  3,000,000  acres.  This  is 
about  one-fifteenth  of  the  amount  of  land  that  can  be 
so  developed. 

Waterfalls  and  rapids  furnish  water  power  that  may 
be  used  for  manufacturing  purposes.  The  available 
coal  supply  in  the  United  States  is  limited.  As  the 
age  of  coal  formation  is  past,  it  is  evident  that  the 
supply  will  some  day  be  exhausted.  When  this  time 
comes  it  will  necessitate  another  source  of  power.  At 


184  -A  YEAR  IN  SCIENCE 

the  present  time,  in  the  United  States,  about  26,000,000 
horse  power  is  developed  from  coal  and  about 
5,500,000  horse  power  from  water.  The  amount  of 
water  power  capable  of  being  developed  by  the  streams 
of  the  country  depends  upon  the  condition  of  the 
rivers,  whether  they  be  at  low  or  'high  water  stage. 
It  is  estimated  that  the  streams  in  their  low  water 
stage  will  fur-nish  almost  40,000,000  horse  power.  This 
is  much  more  than  the  total  amount  generated  now, 
but  the  demands  for  power  will  increase  as  the 
country  grows. 


Questions 

1.  In  what  ways  is  the  rain  which  falls  upon  the 
ground  disposed  of? 

2.  Upon  what  conditions  does  the  erosive  power 
of  a  stream  depend? 

3.  How  much  sediment  has  it  been  estimated  that 
the  Mississippi  Kiver  carries  into  the  Gulf  of  Mexico 
every  day? 

4.  Why    is    this    considered    a    great   loss    to    the 
country  ? 

5.  Suggest  practical  methods  for  preventing  soil 
erosion. 

6.  Describe  fully  the  stages  through  which  a  river 
passes  in  its  development  from  youth  to  old  age. 

7.  If  possible,  name  and  locate  rivers  which  are 
examples  of  these  different  stages. 

8.  How  do  you  account  for  the  fact  that  Niagara 
Falls  is  receding? 


STREAMS  AND  THETR  WORK  185 

9.     What  is  a  flood  plain?     Give  examples  of  flood 
plains. 

10.  Describe  some  of  the  accidents  which  occur  to 
rivers  during  their  life  history. 

11.  What  is  meant  by  a  drowned  river  valley  ?  Give 
examples  of  rivers  having  such  valleys. 

12.  How  do  you  account  for  the  fact  that  so  many 
of  our  large  cities  are  located  on  rivers? 

13.  Why  are  streams  not  of  so  much  importance  as 
a  means  of  travel  as  they  formerly  were  ? 

14.  How  can  you  account  for  the  fact  that  rail- 
roads   have    so    frequently    been    built    along    water 
courses  ? 

15.  Can  you  think  of  any  objections  to  having  rail- 
roads along  water  courses  ? 

16.  About  how  many  acres  of  land  are  now  being 
irrigated  in  the  United  States? 

17.  If  possible,   ascertain  the   value   of  the   crops 
grown  upon  this  irrigated  land. 

18.  To   what   extent  is   water  power   used   in  the 
United  States  for  manufacturing  purposes? 


CHAPTER  XXIV 
SOIL 

Introduction.  Soil  to  most  people  simply  means  a 
layer  of  dirt  covering  the  surface  of  the  earth;  some- 
thing necessary  perhaps,  yet  objectionable  because  of 
the  dust  that  it  produces  in  drought,  and  mud,  in  rainy 
weather.  Yet  this  same  dirt  is  one  of  the  substances 
indispensable  to  all  life.  If  a  sample  of  soil  be  taken 
from  almost  any  place  on  the  surface  of  the  earth  and 
examined  carefully,  it  will  be  found  to  be  largely  a 
layer  of  sand  and  clay  mixed  with  more  or  less  decayed 
animal  and  vegetable  matter.  This  surface  layer  is 
less  than  one  foot  in  depth  over  the  greater  portion  of 
the  earth's  surface,  yet  in  places  it  extends  to  a  depth 
of  several  feet.  Beneath  the  soil  is  a  layer  of  more  com- 
pact earth  containing  less  of  the  decayed  organic  mat- 
ter and  usually  lighter  in  color.  This  layer  is  called 
sub-soil  and  grades  down  gradually  into  the  solid  rock, 
called  the  bed  rock,  from  which  all  soil  originally  came. 

Origin.  From  60%  to  95%  of  the  weight  of  ordinary 
soil  consists  of  rock  fragments.  The  fragments  have 
come  either  from  the  layer  of  rock  bed  just  below  the 
sub-soil,  in  which  case  it  is  called  residuary  or  seden- 

186 


SOIL  187 

tary  soil,  or  from  the  rock  bed  at  a  distance  and 
brought  down  by  running  streams  or  other  agents,  and 
called  drift  or  transported  soil. 

To  produce  soil  many  agents  in  nature  are  at  work, 
the  chief  of  which  are  water,  wind,  plants,  and  animals. 

The  wearing  off  of  the  rock  by  water  and  air  is  called 
weathering.  The  oxygen  of  the  air  combines  readily 
with  other  elements  in  the  rocks  to  form  new  com- 
pounds, which  break  away  from  the  surface.  This 
action  is  very  similar  to  the  rusting  of  iron.  All  are 
familiar  with  the  small  flakes  of  rust  thus  produced. 
Similar  flakes  are  formed  011  the  surface  of  the  rocks. 
This  is  a  slow  process,  to  be  sure,  but  in  the  course  of 
the  ages  that  this  process  has  been  at  work,  great 
changes  have  been  effected.  The  air,  as  wind,  sweeps 
up  the  smaller  particles  of  sand  and  earth  and  whips 
them  together  and  against  the  surface  of  projecting 
rock,  thereby  grinding  the  smaller  particles  finer  and 
also  wearing  off  the  surface  of  the  larger,  harder 
rocks. 

Water  has  great  power  of  dissolution  and  dissolves 
the  more  soluble  compounds  out  of  the  rocks,  thereby 
weakening  and  eventually  breaking  them  up  into 
smaller  pieces.  Pure  water  dissolves  but  slowly,  but  all 
soil  water  usually  has  taken  on  carbon  dioxide  as  it 
came  down  through  the  air,  or  acids  from  the  soil  01 
roots  of  plants,  which  make  it  a  most  powerful  disin 
tegrating  agent. 

Wherever   water   seeps   through   the   soil   into   the. 


188  A  YEAR  IN  SCIENCE 

cracks  and  crevices  of  rocks,  it  slowly  but  surely  dis- 
solves some  of  the  more  soluble  compounds  out  of 
them,  and  carries  them  in  solution  to  some  other  place. 


Fig.  71.  Rock  has  been  dissolved  and  carried  away  by  water 
forming  this  underground  channel.  Water  from  a  higher  level 
slowly  passes  into  this  channel  through  cracks  in  its  walls.  As 
this  water  evaporates,  deposits  like  those  shown  on  the  sides  and 
top  are  left. 


This  is  seen  when  the  water  comes  to  the  surface  again, 
as  it  does  in  a  spring,  which  in  some  instances  leaves 
a  deposit  of  the  dissolved  minerals  in  a  layer  around 
its  mouth. 

The  carrying  power  of  water  is  an  important  factor 
in  producing  and  transporting  soils.  With  every  rain 
some  of  the  water  "runs  off"  of  the  surface,  carrying 


SOIL 


189 


particles  of  soil  and  rock  with  it  into  the  valleys  and 
ravines.  When  the  stream  is  swollen  and  the  current 
swift,  large  rocks  are  carried,  and  as  they  are  rolled 
along,  they  wear  off  the  bottom  and  the  sides  of  the 


Copyright  by  Henry  G.  Peabody. 

Fig.  72.  Top  of  Jupiter  Terrace,  Yellowstone  Park.  Hot  water 
carrying  mineral  matter  in  solution  comes  to  the  surface  in  the 
upper  terraces.  It  then  flows  over  the  surface,  and  as  it  cools 
the  mineral  matter  is  deposited. 


river  bed,  break  off  the  edges  of  other  rocks  against 
which  they  strike,  and  grind  the  finer  rock  particles 
into  'the  mealy  powder  which  makes  up  the  soil.  As 
the  current  slackens  it  drops  its  load,  the  larger,  coarser 
particles  first,  with  the  finer  particles  on  top. 

This  may  be  seen  on  any  bottom  land  after  the  floods 
have  subsided.  The  frequent  floods  of  these  lands 
account  for  their  unusual  fertility.  Rocks  are  further 
broken  up  by  alternate  freezing  and  thawing.  The 
water  which  has  been  absorbed  into  rock  freezes,  and 


190  A  YEAR  IN  SCIENCE 

as  the  ice  expands  it  eventually  splits  and  crumbles 
the  rock  into  many  smaller  pieces. 

Kinds.  Since  the  surface  of  the  earth  originally  was 
solid  rock  and  water,  it  is  evident  that  soil  is  the  prod- 
uct of  decayed  rock,  together  "with  the  remains  of  de- 
cayed plant  and  animal  life. 

In  the  weathering  of  rocks  we  find  two  kinds  of  soil 
resulting.  The  fine,  soft  powder,  or  rock  flour,  is  called 
clay;  while  the  hard,  loose,  insoluble  particles  form 
sand. 

Clay.  Clay,  when  dry,  is  a  powdery  substance ;  when 
wet,  it  is  sticky  and  plastic,  and  easily  molded.  It 
takes  up  water  slowly  and  when  thoroughly  wet  be- 
comes compact  and  solid,  difficult  to  cultivate  and  diffi- 
cult for  the  roots  of  plants  to  penetrate. 

It  is  equally  slow  to  give  up  the  moisture  once  ab- 
sorbed. When  thoroughly  wet  it  is  able  to  hold  as 
much  as  40%  of  its  weight  of  water.  Thus  in  wet 
weather  it  may  hold  too  much  water  for  good  growth, 
while  in  drought  it  may  bake  and  become  too  difficult 
for  roots  of  plants  to  penetrate. 

Air  in  the  soil  is  necessary  for  plant  life.  Although 
clay  is  finely  powdered  and  affords  great  pore  space, 
because  of  the  smallness  of  the  spaces,  air  moves  about 
in  it  with  difficulty,  aerating  it  but  poorly. 

Sand.  Sand  is  made  up  of  hard  separate  particles. 
It  is  loose  and  gritty,  absorbs  water  readily,  and  gives 
it  up  just  as  readily.  It  often  contains  less  than  5% 
of  water.  When  wet  the  particles  of  sand  are  some- 


SOIL  191 

what  loosely  held  together  in  a  mass,  and  when  dry 
it  does  not  bake  nor  crack,  but  returns  to  its  loose 
granular  form. 

The  larger  particles  of  sand  afford  larger  spaces 
between  their  particles,  thereby  permitting  air  to  cir- 
culate among  them  quite  freely. 

The  roots  of  plants  have  no  difficulty  in  penetrating 
sand,  but  because  of  the  looseness  of  its  particles  and 
the  ease  with  which  they  shift  about,  most  plants  are 
unable  to  get  started  in  it.  Thus  sand  alone  is  an 
unsuitable  soil  for  plants.  To  verify  this  you  need 
but  recall  the  almost  lack  of  vegetation  on  sand  dunes. 

The  material  in  the  soil  which  comes  from  the  decay 
of  organic  matter  is  called  humus,  or  leaf-mold.  It  is 
dark  in  color  and  makes  up  a  large  part  of  the  soil  of 
heavily  shaded  forests.  The  humus  part  of  soil  is  very 
important.  It  teems  with  microscopic  plant  and  animal 
forms  so  necessary  in  the  soil  to  the  life  of  green 
plants. 

From  the  fact  that  pure  clay  is  difficult  for  the  roots 
of  plants  to  penetrate  and  sand  alone  may  shift  too 
frequently  for  plants  to  become  established,  it  is  appar- 
ent that  neither  alone  is  an  ideal  soil  for  plants,  though 
either  may  be  abundantly  supplied  with  the  minerals 
and  water  necessary  for  plant  life. 

For  most  plants,  the  best  soil  is  a  combination  of 
clay,  sand,  and  humus. 

A  soil  of  equal  parts  of  clay  and  sand  with  some 
humus  is  called  loam. 


192  A  YEAR  IN  SCIENCE 

Based  upon  the  proportions  of  sand  and  clay  in  soils, 
Dryer  gives  the  following  classification : 

.Sandy  soil 80%  sand        10%   clay 

Sandy   loam    60-70%      "       10-25%     '' 

Loam    40-60%      "      15-30%     " 

Clay  loam   10-35%      "      30-50%     '• 

Clay    10%      "      60-90%     " 


Questions 

1.  What  is  soil?    Sub-soil? 

2.  What  is  the  origin  of  all  soil? 

3.  What  is  residuary  soil? 

4.  What  is  drift  soil? 

5.  What  are  the  chief  agents  in  the  production  of 
soil  ?  Explain  fully  the  -work  of  each. 

6.  How  do  clay  and  sand  differ? 

7.  Does  either  alone  make  a  satisfactory  soil  for 
plants?    Give  reason  for  your  answer. 

8.  What  then  is  a  good  combination? 

9.  Give  Dryer's  classification  of  soils. 


CHAPTER  XXV 

1XTRODUCTIOX  TO  PLAXTS 

Importance  of  plants.  So  far  we  have  confined  our- 
selves entirely  to  a  consideration  of  the  physical 
sciences.  In  other  words,  we  have  studied  the  facts 
and  laws  dealing  with  things  which  are  not  living, — 
inorganic  matter.  It  is  of  equal  interest  and  impor- 
tance to  know  something  about  the  living,  organic 
things,  plants  and  animals,  including  ourselves. 

First,  we  shall  study  plants.  To  appreciate  the  im- 
portance of  plants  to  man,  let  us  consider  the  uses  we 
make  of  them  in  our  homes.  Our  houses  are  built,  in 
part  at  least,  of  wood;  the  furniture  in  them  is  largely 
of  wood :  the  fuel  we  burn,  the  food  we  eat,  and  much 
of  the  clothing  which  we  wear  are  derived  from  plants. 
Thus  we  depend  for  shelter,  warmth,  clothing,  and 
even  for  food  upon  the  many  green  plants  growing 
about  us. 

Neither  should  we  forget  nor  underrate  how  much 
plants  add  to  the  enjoyment  of  life.  Imagine  for  a 
moment  that  there  were  no  green  grass,  no  trees,  no 
fruits  and  no  flowers.  "What  a  dreary,  desolate  place 
the  world  would  be  ! 

A  knowledge  of  the  plant  life  about  us  is  interesting 

193 


194 


A  YEAR  IN  SCIENCE 


and  useful.  Everything  which  we  learn  adds  a  new 
interest  to-  our  lives.  Consider  for  a  moment  what  you 
know  about  the  plants  which  you  see  each  day  as  you 
go  to  and  from  school.  How  do  these  plants  live? 
Do  they  breathe?  What  kind  of  food  do  they  require, 
and  how  does  this  food  reach  the  topmost  leaf  011  a 
large  tree  ?  To  answer  these  and  many  other  questions 
will  afford  you  pleasure  and  satisfaction  in  your  study 
of  plants. 


Photograph  by  Henry  G.  Peabody. 
Fig.  73,     A  California  garden. 

The  vegetation  about  us  is  abundant  and  of  great 
variety.  There  are  trees,  shrubs,  vines,  herbs,  mosses, 
ferns,  mushrooms,  and  many  other  kinds  of  plants. 
They  vary  in  size  from  our  largest  trees,  over  300  feet 
high,  to  forms  so  small  that  they  can  not  be  seen  without 


INTRODUCTION  TO  PLANTS  195 

the  aid  of  a  microscope.  But  no  matter  what  their  size, 
form,  or  general  structure  is,  they  all  require  much 
the  same  conditions  to  live.  Just  as  human  life, 
whether  in  America,  Africa,  Japan,  or  Australia,  de- 
pends upon  food,  air,  and  water,  so  plant  life,  too, 
depends  upon  food,  air,  and  water. 

In  our  study  of  plants  we  shall  consider  principally 
what  they  do,  and  how  they  do  it.  The  work  which 
any  machine  does  is  a  direct  result  of  the  way  in 
Avhich  it  is  constructed.  It  is  necessary,  for  example, 
to  know  the  structure  of  an  automobile  before  it  is  pos- 
sible to  understand  how  it  runs.  Similarly  we  must 
know  much  about  the  structure  of  plants,  before  we 
can  understand  how  they  work. 

Plants  are  composed  of  cells.  Much  life  of  which  we 
are  ordinarily  quite  unconscious  exists  about  us.  For 
instance,  if  we  examine  under  a 
microscope  some  scum  taken  from 
a  pond,  we  shall  find  in  it  many 
small  animals  and  plants.  Among 
these  will  be  found  some  of  the 
simplest  living  things.  Upon  closer 
examination  each  of  these  small 
living  things  will  be  found  to  be  Fig  74  P7e?/,.ococ. 

,    .  ,,.  ,    -,  ,     -,  cus,  a  one  celled  plant. 

round  in  outline  and  bounded  on     A.  a   single   ceil;    B, 

clusters  of  cells. 

the   outside  by   a  thin  membrane, 

r-alled  the  cell  wall.  "Within  this  is  a  thin,  watery 
substance  somewhat  granular  in  appearance,  known  as 
•protoplasm.  In  the  protoplasm  is  a  denser  spot,  a  more 


196 


A  YEAR  IX  SCIENCE 


Nucleus 


Cell  wall- 


complicated  structure,  the  nucleus.  Protoplasm  is  the 
living  part  of  the  cell.  These  three  parts,  the  cell  wall, 
the  protoplasm,  and  the  nucleus,  are  the  cell. 

The  simplest  form  of  plant  or  animal  life  has  only 

one  cell.  Others  have  sev- 
eral cells  grouped  together, 
and  still  others  consist  of 
millions  of  cells.  When  a 
plant  consists  of  but  a  few 
cells,  these  cells  are  very 
vacuoie  similar  in  structure.  How- 
ever, when  millions  of  cells 

Protoplasm-^  $  are    present,-  as    in    trees, 

there  is  much  variation  in 
them.     Some  of  them  are 
of  one  kind  and  form  the 
Fig.   75.     Diagram   of  a  plant    bark    of    the    tree,    others 

form  the  wood,  others  form 

tubes  through  which  liquids  travel,  and  still  others  are 
used  to  store  food.  Each  group  of  similar  cells  is  called 
a  tissue.  For  example,  wood  is  one  kind  of  a  tissue; 
the  outer  covering  of  a  leaf  is  another  kind  of  tissue ; 
and  bark  is  still  another  tissue.  In  all  cases,  while  the 
plant  is  alive,  the  tissues  are  composed  of  cells  which 
contain  the  living  substance,  protoplasm. 

Composition  of  protoplasm.  What  is  protoplasm? 
Exactly  what  is  its  composition?  Why  is  it  living? 
How  does  it  grow?  These  and  similar  questions  we 
can  not  fully  answer.  They  still  remain  to  us  the  un- 


Chloroplast 


INTRODUCTION  TO  PLANTS  197 

answered  riddle  of  life.  We  do  know  something  about 
the  chemical  composition  of  protoplasm.  We  know 
that  it  is  a  very  complex  compound ;  that  is,  it  contains 
many  elements.  The  chief  elements  are  carbon,  hydro- 
gen, oxygen,  and  nitrogen.  Sulphur,  phosphorus,  iron, 
potassium,  calcium,  silicon,  and  minute  quantities  of 
other  elements  are  also  found  in  its  composition. 

Properties  of  protoplasm.  Although  the  living  mat- 
ter of  which  both  plants  and  animals  are  composed  is 
almost  impossible  of  correct  analysis,  we  do  know  that 
it  possesses  certain  properties  which  inorganic  matter 
does  not  possess.  These  properties  are  as  follows: 

1.  Protoplasm  grows.     It  has  the  wonderful  power 
of  taking  in  food  material  and  then  changing  it  from 
a  non-living  substance  into  living  protoplasm. 

2.  Protoplasm  breathes.     It  can  take  in  oxygen  with 
which  it  unites  to  produce  the  heat  and  energy  necessary 
for  movement  and  other  activities. 

3.  Protoplasm  can  rid  itself  of  waste  materials. 
Substances,  which  are  of  no  use  to  them,  collect  in 
organisms,  and  are,  in  turn,  thrown  off. 

4.  It  is  sensitive  to  influences,  or  stimulations,  from 
without  its  own  substances.  Light,  heat,  electricity, 
and  other  stimuli  Avill  cause  protoplasm  to  move. 

.I.  Protoplasm  can  reproduce  itself.  Cells  can  divide 
and  form  other  cells.  Plants  are  constantly  appearing 
to  take  the  place  of  those  that  die. 

Comparison  of  plants  and  animals.  From  observa- 
tions, we  are  all  familiar  with  many  living  organisms. 


198  A  YEAR  IN  SCIENCE 

Some  of  these  we  call  plants  and  others  animals.  The 
question  naturally  arises :  What  are  the  differences 
betAveen  these  two  groups  of  organisms?  We  have 
just  learned  that  the  difference  is  not  one  of  compo- 
sition, for  in  each  the  living  substance  is  protoplasm. 
The  difference  most  evident,  is  in  the  relative  powers 
of  motion.  Animals,  we  may  say,  can  move  from  place 
to  place,  but  plants  can  not.  This  difference,  however, 
does  not  hold,  for  some  animals  are  attached  and  can 
not  move.  The  more  common  of  such  animals  are 
corals  and  sponges.  Motion  is  also  present  in  plants. 
If  a  plant  is  placed  in  front  of  a  window  the  leaves 
move  toward  the  light ;  a  root  will  move  toward  water ; 
and  the  cells  (spores)  from  which  some  plants  are 
formed  are  capable  of  swimming  about  as  rapidly  as 
some  animals  do. 

The  chief  difference  between  plants  and  animals  is 
one  depending  upon  the  kind  of  food-materials  which 
each  requires.  Plants,  wre  already  know,  secure  some 
of  their  raw  food-materials  from  the  soil.  It  is  com- 
monly believed  that  they  secure  most  of  their  food 
supply  from  this  source,  but  this  is  not  Avholly  correct. 
The  plant  takes  water  from  the  soil,  and  a  very  small 
part  of  the  soil  itself  is  used.  The  remainder  of  the 
materials  required  are  supplied  by  the  air  in  the  form 
of  carbon  dioxide.  Out  of  these  raw  materials,  water, 
carbon  dioxide,  and  small  quantities  of  minerals  from 
the  soil,  a  plant  is  able  to  make  its  own  food.  An  ani- 
mal, on  the  other  hand,  can  not  make  its  food. 


INTRODUCTION  TO  PLAXTS  199 

From  another  point  of  view,  we  find  that  the  dif- 
ferences between  the  food  habits  of  plants  and  animals 
is  not  in  the  substances  which  they  require,  but  in  the 
way  they  secure  them.  Starch  and  sugar,  for  example, 
form  an  important  part  of  both  plant  and  animal  food. 
The  animal  secures  this  starch  from  a  plant  or  some 
other  source  in  which  it  is  all  ready  to  be  used.  The 
plant,  however,  manufactures  its  own  starch  and  sugar 
out  of  very  simple  substances,  water  (H20)  and  carbon 
dioxide  (C02).  The  parts  of  the  plant  in  which  the 
starch  is  made  are  the  leaves. 

Questions 

1.  What  are  the  principal  plants  used  by  man  for 
food?    For  clothing?    For  fuel? 

2.  Explain  other  uses  of  plants  to  man  in  addition 
to  the  uses  for  food,  clothing,  and  fuel. 

3.  May  a  knowledge  of  plants  be  of  any  value  to 
you  apart  from  its  value  in  making  a  living? 

4.  Name  the  trees  with  which  you  are  familiar. 

5.  When  do  the  leaves  first  appear  on  these  trees? 

6.  Name  the  wild  flowers  you  have  noticed. 

7.  What  is  the  largest  plant  which  you  have  seen? 
The  smallest? 

8.  What  are  the  three  things  necessary  to  plant 
life?    Are  they  also  necessary  to  your  life? 

9.  What  is  a  cell?    What  are  its  parts? 

10.  What  is  a  tissue?    Give  examples. 

11.  What    is    known    about    the    composition    of 
protoplasm?    State  five  properties  of  protoplasm. 

12.  Explain  fully  the  chief  differences  between  plants 
and  animals. 


CHAPTER  XXVI 


LEAVES 

Structure  of  leaves.  It  is  necessary  to  know  some- 
thing about  the  structure  of  leaves  in  order  to  under- 
stand the  method  by  which  they  carry  on  the  processes 
which  make  them  such  important  parts  of  plants.  You 
already  know  that  a  leaf  has  a 
broad  part  of  green  color,  the 
blade.  Most  leaves  also  have  a 
stem-like  part,  the  petiole.  Some- 
times two  leaf-like 
parts,  stipules,  are 
present  at  the  base 
of  the  petiole.  The 
blade  may  take  al- 
most any  conceiv- 
able shape,  but  it 
is  always  strength- 
ened by  a  frame- 
work of  tubes 

called  veins.  These  veins  are  con- 
tinuous with  tubes  passing  through 
the  petiole  and  down  through  the 
stem  of  the  plant  into  the  root.  Veins 

200 


Petiole 


Fig.   76.     Apple  leaf, 
net-veined. 


Fig.  77.  Leaf 
o  f  lily-of-the-. 
valley,  parallel- 
veined. 


LEAVES 


201 


usually  present  a  netted  appearance,  but  in  some  leaves, 
such  as  those  of  lilies  and  grasses,  they  run  in  somewhat 
parallel  lines. 

When  examined  under  a  microscope,  each  leaf  is 
found  to  be  composed  of  an  almost  countless  number 
of  cells,  which  vary  in  structure  and  in  use.  The  outer 
surface,  or  epidermis,  of  the  leaf  is  composed  of  large 
irregular-shaped  cells.  The  interior  of  the  leaf  is  filled 
between  the  veins  with  loosely  arranged  cells  forming 
what  is  known  as  the  mcsophyll.  The  epidermis, 


-)— Pafisade 
ssue 


Spongy 
Tissue 


Chamber 


Fig.  78.     Cross  section  of  a  leaf  of  a  barberry  showing  the  internal 
structure, 

although  frequently  very  thin,  serves  as  a  protection 
to  the  mesophyll,  which  is  easily  crushed  and  dies 
quickly  when  the  epidermis  is  removed.  In  the  epi- 
dermis, on  the  under  surface  of  the  leaf,  there  are  a 
number  of  tiny  oval  openings.  These  are  called 


202 


A  YEAR  IN  SCIENCE 


stomates.  (The  Greek  word  stoma  means  mouth.)  On 
each  side  of  a  stomate  there  is  a  kidney-shaped  cell 
called  a  guard  cell.  The  shape  of  these  cells  can  be 

changed  and  in  so  do- 
ing the  openings  into 
the  leaf  can  be  made 
smaller  or  larger.  It 
is  not  exactly  clear  of 
just  what  service  this 
is  to  the  leaf.  There 
are  thousands  of  sto- 
mates on  each  leaf, 
usually  only  on  the 
under  surface.  Gases 
pass  in  and  out  of 
the  leaf  through  the 
stomates.  A  cross- 
section  of  a  leaf  shows 
that,  immediately  below  the  epidermis,  there  is  a  row  of 
green  cells  closely  packed  together.  Below  these  are 
the  large,  green,  loosely-arranged  cells  of  the  meso- 
phyll.  The  stomates  open  directly  into  the  spaces,  air 
chambers,  formed  between  these  cells. 

Chlorophyll.  Some  things  in  nature  are  so  common 
that  we  do  not  stop  to  study  them;  we  take  them  for 
granted.  We  know  that  most  plants  have  a  great 
many  leaves  and  that  these  leaves  are  green.  "We  per- 
haps have  never  considered  the  nature  or  importance 
of  this  green  color.  Inside  of  all  the  cells  of  the  leaves, 


Fig.  79.  Epidermis  of  a  leaf  of 
geranium  showing  stomates ;  c,  cell ; 
p,  opening  of  stomate  ;  gc,  guard  cell. 


LEAVES  203 

except  those  of  the  epidermis,  there  are  a  number  of 
green  colored  bodies  called  chloroplasts.  They  are  prin- 
cipally composed  of  protoplasm  by  which  a  green  sub- 
stance, chlorophyll,  is  manufactured.  (Chloron,  green; 
phyUon,  leaf.)  The  chlorophyll  gives  the  green  color 
to  the  chloroplast.  It  is  upon  the  presence  of  this  sub- 
stance that  the  most  important  work  of  the  plant 
depends,  and  upon  that  work  all  life,  including  our  own, 
depends.  Think  of  the  significance  of  this  fact. 

Food  making.  We  have  already  stated  that  a  plant 
uses  as  a  part  of  the  raw  materials,  from  which  to  make 
its  food,  carbon  dioxide  and  water.  Out  of  these  in- 
organic materials  leaves  can  manufacture  starch;  this 
is  their  principal  function.  The  water  is  obtained 
from  the  soil  and  passes  up  through  bundles  of  tubes 
from  the  roots  to  the  veins  of  the  leaves.  Carbon 
dioxide  from,  the  air  enters  through  the  stomates.  The 
carbon  dioxide  and  water  are  then  combined  to  form 
starch  or  sugar.  Starch  and  sugar  belong  to  a  group 
of  foods  known  as  the  carbohydrates,  which  are  com- 
posed of  carbon,  hydrogen,  and  oxygen.  They  always 
contain  twice  as  much  hydrogen  as  oxygen.  To  form 
carbohydrates  from  the  raw  materials  we  know  that 
chloroplasts  and  light  are  essential.  By  means  of 
protoplasm  and  chlorophyll,  chloroplasts  absorb  energy 
from  the  sun's  rays.  With  this  energy,  the  chloro- 
plasts are  able  to  break  the  compounds,  water  and 
carbon  dioxide,  into  carbon,  hydrogen,  and  oxygen,  the 
elements  of  which  they  are  composed.  These  three  ele- 


204 


A  YEAR  IN  SCIENCE 


Fig.  80.  Experi- 
ment to  show  that 
oxygen  is  given  off 
by  green  plants  in 
the  sunlight. 


ments  then  immediately  unite  and 
finally  form  sugar  and  starch.  The 
exact  chemical  processes  which  this 
involves  are  not  completely  known. 
Carbohydrates  contain  twice  as  much 
hydrogen  as  oxygen.  Carbon  dioxide 
(C02)  and  water  (H20)  contain  only 
two  parts  of  hydrogen  for  every  three 
of  oxygen.  Consequently  there  is  an 
excess  of  oxygen  in  this  process. 
This  oxygen  is  given  off  as  a  by- 
product. The  process  of  starch-mak- 
ing may  be  expressed  with  the  follow- 
ing chemical  equation : 

N  (6C02)  +  N  (5H20)  ==  N  (CCH1005)  +  N  (602) 

Carbon  dioxide  +  water  =  starch  +  oxygen 
On  bright  days  starch  is  formed  very  rapidly.  Dur- 
ing the  night  this  food  is  transformed  into  soluble 
forms  and  then  moves  from  the  leaf  to  other  parts  of 
the  plant.  Much  of  this  is  stored  away  in  the  form 
of  starch  in  such  parts  of  plants  as  the  seeds  of  cereals, 
grains,  fruits,  potato  tubers,  etc.  From  these  all  animals 
derive  food.  Upon  this  starch-making  process  of  the 
green  plants  all  life  is  dependent  for  the  ultimate 
source  of  food.  Carbohydrates  make  up  a, very  large 
part  of  the  food  of  all  animals.  Indirectly  the  meat 
which  we  eat  is  derived  from  these  carbohydrates  made 
by  plants.  Beef,  for  example,  is  procured  directly  from 


LEAVES  205 

cattle,  but  they  in  turn  feed  upon  various  kinds  of 
plants  or  parts  of  plants. 

Food  storage.  We  frequently  think  of  potatoes,  car- 
rots, onions,  radishes,  sweet  potatoes,  beets,  fruits, 
seeds,  etc.,  as  food  for  ourselves.  No  doubt  it  has 
never  occurred  to  most  of  us  that  these  parts  are  of 
real  use  to  the  plants  on  which  they  are  formed.  As 
food  is  manufactured  by  the  plant  it  is  disposed  of 
in  either  of  two  ways.  It  may  be  used  immediately 
for  repair  and  growth,  or  it  may  be  stored  and  some  of 
it  may  subsequently  be  used  by  the  plant. 

Food  may  be  stored  in  almost  any  part  of  the  plant, 
but  in  many  plants  this  storage  takes  place  in  parts 
underground,  either  roots  or  underground  stems.  Such 
parts  are  the  beet,  turnip,  carrot,  parsnip,  radish,  onion, 
potato,  and  sweet  potato.  This  stored  food  is  often 
consumed  by  the  plant  for  growth  during  the  early 
part  of  the  following  season.  Seeds  and  fruits  also 
serve  as  places  for  food  storage.  Small  plants  depend 
at  first  for  their  growth  upon  this  reserve  food  in  the 
s^eds  from  which  they  were  produced. 

Because  of  the  great  amount  of  food  present  in  pota- 
toes, carrots,  etc.,  and  in  all  kinds  of  seeds,  such  as 
wheat,  corn,  rye,  oats,  and  in  fruits,  these  parts  serve 
as  the  most  important  articles  of  food  for  men  and 
other  animals.  These  food  storage  parts  are  used 
directly  or  else  products  are  manufactured  from  them, 
such  as  oatmeal,  cornmeal,  flour,  corn  starch,  and 
tapioca.  The  economic  importance  of  plants  in  trades 


206 


A  YEAR  IN  SCIENCE 


and  industries  can  scarcely  be  estimated.  The  accom- 
panying table  will  be  of  some  value  in  helping  you  to 
appreciate  their  importance : 

VALUE  OF  CROPS  IN  THE  UNITED  STATES  IN  1909* 


Crop 

Value 

Crop 

Value 

All    crops  
Cereals     
Corn   . 

$5,487,161,223 
2,665,539,714 
1,438,553,919 

Fruits  and  nuts. 
Strawberries     . 
Blackberries 

.$    222,024,216 
17,913,926 

Oats 

414,697,422 

and     dewber- 

Wheat 

657,656,801 

ries  

3,909,831 

Other  grains  and 

07  536  085 

Orchard  fruits  .  .  . 
Apples 

140,867,347 
83,231,492 

Dry  beans  
Dry  peas  
Peanuts 

21,771,482 
10,963,739 
18271  929 

Pears    
Cherries  
Grapes             .  . 

7,910,600 
7,231,160 
•22,027.961 

Cotton  and  cot- 
ton   seed.  .  .  . 
Vegetables     
Potatoes    

824,696,287 
418,110,154 
166,423,910 

Nuts    

4,447,674 

*Thirteenth  Census  of  the  United  States,   1910. 

Other  foods  manufactured  by  plants.  Other  foods, 
proteins,  are  manufactured  by  the  plants  from  the 
carbohydrates  and  the  various  substances  which  come 
up  from  the  soil.  These  mineral  substances,  which  are 
dissolved  in  soil  water,  are  called  solutes.  Proteins  con- 
tain carbon,  hydrogen,  oxygen,  nitrogen,  and  in  addi- 
tion small  quantities  of  many  other  elements.  These 
are  all  combined  to  form  a  very  complex  compound 
which  is  more  like  protoplasm  than  any  other  non- 
living substance.  We  do  not  know  how  plants  manu- 
facture proteins.  They  appear  to  add  nitrogen  and 
other  substances  from  the  soil  to  the  carbohydrates. 
We  have  before  referred  to  the  fact  that  it  is  essential 


LEAVES  207 

that  the  soil  contains  soluble  nitrogen  compounds  (see 
page  103).  We  now  know  the  use  of  this  nitrogen. 

Uses  of  food.  You  know  that  to  live  you  must  have 
food.  You  know,  too,  that  this  food  must  be  digested 
and  taken  to  all  parts  of  your  body.  There  it  must 
be  changed  from  non-living  into  living  material  to  be 
used  for  growth,  repair,  or  oxidation  to  produce 
heat  and  energy.  In  order  to  make  this  possible,  you 
need  air  as  well  as  food.  In  connection  with  the 
changes  which  take  place  in  the  wearing  out  and  the 
building  up  of  parts  of  the  body  and  in  the  formation 
of  energy,  certain  waste  substances  are  formed.  These 
are  harmful  to  the  body  and  must  be  gotten  rid  of. 
The  entire  process  necessary  to  keep  you  alive  is  known 
as  the  process  of  nutrition. 

A  plant,  likewise,  must  carry  on  this  process  of 
nutrition.  From  carbon  dioxide  from  the  air,  water, 
and  solutes  from  the  soil,  and  energy  from  the  sun, 
the  plants  make  their  own  food.  After  they  have 
manufactured  their  food  they  are  then  ready  to  take 
up  the  processes  of  nutrition  just  where  we  do  after 
food  is  eaten.  Their  food  must  be  digested.  By  that 
we  mean  that  it  must  be  transformed  into  soluble  form 
so  that  it  can  be  transferred  to  all  parts  of  the  plant. 
A  wonderful  process  then  takes  place.  This  digested 
food  is  made  into  protoplasm.  The  exact  nature  of  the 
chemical  processes  which  this  involves  we  do  not  know, 
but  in  some  way  this  non-living  food  material  is  made 
into  living  protoplasm.  Evidently  this  process  can  be 


208 


A  YEAR  IN  SCIENCE 


carried  011  only  by  living  material,  for  man  has  never 
succeeded  in  producing  living  from  non-living  material. 
Transpiration.  Water  plays  an  important  part  in 
the  life  of  plants.  It  is  the  most  important  single 
factor  which  determines  the  way  plants  grow  and 
where  they  grow.  All  plant  activity  depends  upon  its 
presence  in  considerable  amount.  Although  there  is 
great  and  continual  need  of  water,  and  although  fre- 
quently the  supply  is  inadequate,  still  there  is  always 
an  enormous  loss  by  way  of  the  surface  of  the  leaves. 
This  evaporation,  or  passing  of  the  water  from  the  leaves, 

is  known  as  transpiration. 
Since  this  water  passes  off  in 
the  form  of  a  gas,  we  are 
usually  not  aware  that  water 
is  constantly  evaporating 
from  the  leaves  of  plants. 
There  are  several  ways,  how- 
ever, by  which  this  can  be 
demonstrated.  When  a  potted 
plant,  the  pot  of  which  has 
been  carefully  wrapped  in 
sheet  rubber  to  prevent  the 
Fig.  si.  Experiment  to  escape  of  moisture,  is  placed 

show    transpiration.      The  . 

water  which  evaporates  under  a  belljar,  Within  a 
from  the  leaves  condenses  on 

few    hours    drops    of    water 

collect  on  the  inside  of  the  belljar.  The  amount  of 
water  lost  by  a  plant  can  be  determined  by  weighing  a 
potted  plant,  so  covered  that  no  moisture  can  escape 


LEAVES  909 

from  the  pot.  If  the  area  of  the  leaves  is  then  ascer- 
tained, it  is  possible  to  know  how  much  water  is 
evaporated  per  day.  per  square  inch.  It  has  been 
estimated  that  a  sunflower  plant  transpires  about  a 
quart  of  water  on  a  warm  day.  A  tree  transpires  a 
great  quantity  of  water,  in  some  cases  as  much  as  175 
gallons  a  day.  The  grass  on  an  average  city  lot  will 
distribute  to  the  air  at  least  half  a  ton  of  water  in  twenty- 
four  hours. 

Disadvantages  of  transpiration.  The  disadvantages 
to  the  plant  of  this  great  loss  of  water  are  very  evident. 
From  personal  observation,  you  know  that  many  plants 
die  because  of  lack  of  water,  which  evaporates  from 
them  more  rapidly  than  they  can  replace  it.  This 
excessive  loss  of  water  is  the  greatest  danger  to  which 
plants  are  exposed,  and  it  renders  necessary  constant 
provision  for  water  in  the  soil  where  plants  grow. 

Advantages  to  plant.  There  is  a  difference  of  opinion 
as  to  the  advantages  of  transpiration  in  plants.  Recent 
experiments  indicate  that  this  process  of  evaporation 
cools  the  leaves  and  thus  prevents  them  from  being 
overheated.  Water  passing  out  of  the  leaves  makes  it 
possible  for  more  water  to  enter  at  the  roots.  As  a 
result,  there  is  a  stream  of  water  passing  through 
the  plant  constantly,  entering  through  the  roots  and 
going  out  through  the  leaves.  This  is  known  as  the 
transpiration  current.  Entering  the  roots  with  the 
water  a#e  solutes,  mineral  substances  in  solution.  These 
solutes  must  pass  from  the  roots  to  the  leaves,  a 


210 


A  YEAR  IN  SCIENCE 


Fig.   82.     An  artificial  water-lily  pond. 

distance  in  some  cases  of  hundreds  of  feet.  When 
passing  through  living  parts  of  the  plant,  these  solutes 
pass  from  one  cell  to  the  next  by  diffusion.  In  the 
larger  plants  the  water  and  solutes  are  carried  part 


LEAVES 

of  the  way  through  tubes  which  are  dead.  In  such 
regions  the  solutes  are  carried  along  in  the  water,  the 
movement  of  which  is  partly  due  to  the  fact  that  a 
constant  stream  is  kept  up  because  of  the  evaporation 
taking  place  at  the  surface  of  the  leaves. 


Photograph  by  Henry  G.  Peabody. 
Fig.  83.     Conditions  in  a  moist,  semi-tropical  forest. 

Habitat  dependent  on  water  supply.  The  conditions 
upon  the  earth's  surface  favorable  for  plant  life  are 
very  diverse.  Plants,  as  a  result,  become  grouped 
according  to  the  conditions  favorable  for  their  growth, 
forming  so-called  plant  associations  or  plant  societies. 
These  associations  are  determined  by  combinations  of 
conditions  such  as  light,  temperature,  and  water. 
Perhaps  the  most  important  single  condition  is  water. 


212  A  YEAR  IN  SCIENCE 

The  amount  of  available  water  varies  from  a  very  small 
supply  in  deserts  to  the  abundant  supply  in  swamps  and 
lakes.  The  character  of  the  soil  also  has  a  very 
important  effect  on  the  water  supply.  Some  soils  retain 
water  and  others  do  not.  The  structure  of  the  plants 
varies  according  to  the  water  supply.  Plants  living 
under  water  differ  greatly  from  those  living  on  land. 


Permission  of  Chicago,  Milwaukee  and  St.  Paul  Railroad. 
Fig.  84.     Type  of  vegetation  found  on  a  mountain  slope. 


Those  which  are  so  constructed  that  they  lose  a  great 
amount  of  water  can  live  only-  under  conditions  where 
the  supply  of  water  is  equal  to  the  loss.  In  some 
regions  plants  must  store  water  to  tide  them  over  long- 
periods  of  drought.  This  is  especially  true  of  desert 
plants,  some  of  which,  such  as  cactuses,  when  cut  open, 
give  out  enough  water  for  men  and  other  animals  to 


LEAVES 


213 


drink.  In  many  such  plants  the  stems  or  roots  are 
greatly  swollen  and  contain  large  quantities  of  water. 
Leaves  also  serve  as  organs  for  water  storage.  The 
thick  leaves  of  century  plants  are  good  examples  of 
this  kind  of  leaf. 

Protection  ag*ainst  loss  of  water.  Plants  have  many 
methods  of  protection  against  excessive  loss  of  water. 
One  of  the  most  evident  methods  is  in  the  reduction  of 
the  size  of  the  leaves.  Plants  such  as  the  heaths, 
which  live  in  very  dry  soils,  have  very  small  leaves. 
In  some  desert  plants,  such  as  cactuses,  the  leaves 


Fig.   80.     A  group  of  cactus  plants. 

are   practically  wanting.     Evaporation   is  frequently 
retarded  hy  modification  of  the  epidermis  of  the  leaves. 


214  A  YEAR  IN  SCIENCE 

The  outer  portion  of  the  cell  walls  contains  a  cork-like 
substance  which  is  waterproof.  The  surface  of  the 
leaves  of  some  plants  is  covered  by  a  film  known  as 
the  bloom.  If  this  is  removed,  evaporation  takes  place 
much  more  rapidly.  You  have  probably  noticed  this 
bloom  on  some  leaves  such  as  the  tulip,  and  certainly 
on  fruits  like  grapes  and  plums.  Sometimes  the  leaves 
are  covered  with  soft  hairs.  In  some  instances,  as  the 
mullein,  these  hairs  are  very  numerous.  They  are  also 
numerous  on  very  young  leaves.  This  is  especially 
evident  on  young  fern  leaves.  These  hairs  are  known 
to  retard  evaporation. 

Stomates  serve  to  admit  air  to  the  interior  of  the 
leaf,  and  they  also  allow  moisture  in  the  form  of  vapor 
to  pass  out.  By  changes  in  the  guard  cells,  the  stomates 
of  many  plants  may  be  opened  and  closed.  When  they 
are  open,  the  gas  exchanges  necessary  for  food-making 
are  facilitated.  This  condition,  however,  also  increases 
transpiration.  The  presence  of  stomates  only  on  the 
under  surface  of  most  leaves  is  probably  an  advantage 
in  reducing  transpiration.  On  leaves  which  stand  erect, 
as  grasses,  they  are  almost  equally  distributed  on  both 
sides,  and  on  those  which  lie  on  the  surface  of  the 
water,  as  the  giant  water  lily,  they  are  present  only 
on  the  upper  surface, 

Many  plants  shed  their  leaves  at  the  beginning  of  a 
cold  or  a  dry  period.  This  is,  no  doubt,  of  great 
advantage  to  the  plant  because  it  results  in  an  enormous 
reduction  of  transpiration.  Plants  which  have  the 


LEAVES 


215 


habit  of  shedding  their  leaves  are  called  deciduous. 
In  temperate  regions  all  plants,  except  the  few  ever- 
greens, shed  their  leaves  in  the  autumn.  As  soon  as 
the  temperature  of  the 'soil 
is  at  the  freezing  point,  the 
plant  can  absorb  very  lit- 
tle water.  When  the  time 
comes  for  shedding  of 
leaves  a  special  layer  of 
tissue  is  formed  at  the 
base  of  the  petiole.  This 
tissue  gradually  cuts  the 
leaf  off  and  at  the  same 
time  covers  the  wound 
which  is  produced.  The 
brilliant  coloration  of  au- 
tumn leaves  is  closely  asso- 
ciated with  the  changes 
which  take  place  in  the 
leaves  previous  to  their 

removal.  The  food  materials  are  withdrawn  from  the 
leaf  before  it  is  shed,  and  the  gradual  reduction  of  the 
activity  of  the  leaves  and  the  breaking-down  processes 
which  take  place  in  the  dying  leaf  produce  the  brilliant 
colors.  These  processes  may  be  caused  by  frost,  but 
not  necessarily  so. 

Respiration.  All  living  things  require  oxygen.  A 
plant  takes  in  oxygen  largely  through  the  stomates  of 
the  leaves,  but  this  function  is  not  limited  to  the  leaves. 


Fig.  86.     A  sycamore  tree  in 
winter  condition. 


216  A  YEAR  IN  SCIENCE 

To  a  less  extent  oxygen  is  also  taken  in  through  the 
stems.  The  oxygen,  after  entering  the  plant,  passes 
by  diffusion 'to  all  parts  of  the  plant,  where  it  is  used 
to  decompose  the  complex  protoplasm,  or  perhaps  food 
materials,  into  simple  substances.  Just  what  chemical 
processes  this  may  involve  we  do  not  know,  but  oxygen 
is  consumed,  complex  plant  substances  are  broken 
down,  and,  as  a  result  of  this  decomposition,  energy  is 
released.  By  means  of  this  energy  plants  are  enabled 
to  perform  their  work.  This  process  results  in  the 
formation  of  various  simple  compounds,  chief  of  which 
are  carbon-dioxide  (C02)  and  water  (H20).  These 
are  waste  products,  and  they  are  passed  off  through  the 
same  organs  that  take  in  oxygen. 

This  process  in  plants  (also  animals)  in  which  oxygen 
combines  with  the  living  tissues  and  releases  energy  is 
known  as  respiration.  It  should  be  kept  distinctly  in 
mind  that  the  exchange  of  gases  in  respiration  in  plants 
is  exactly  the  same  as  that  in  animals.  It  was  once 
customary  to  contrast  plants  and  animals  by  stating 
that  the  former  took  in  C02  and  gave  off  0,  Avhile  the 
latter  took  in  0  and  gave  off  C02.  This  confusion  arose 
because  the  processes  of  food-making  and  respiration 
in  plants  were  not  fully  understood.  In  bright  sun- 
light the  process  of  food-making  takes  place  so  rapidly 
that  it  masks  the  process  of  respiration.  As  a  result, 
plants  in  breathing  were  supposed  to  use  C02  and  to 
give  off  0. 

Air  storage.     In  most  plants  there  is  an  abundant 


LEAVES  217 

supply  of  oxygen  for  respiration,  and  of  carbon  dioxide 
for  carbohydrate  synthesis.  In  stagnant  swamps  and 
undrained  ponds,  however,  the  oxygen  supply  is  often 
very  scant.  In  plants  living  under  such  conditions 
there  are  frequently  present  in  the  interior  of  the  plant 
extensive  air  chambers  for  storing  air.  By  means  of 
this  "inner  atmosphere,"  respiration  and  carbohydrate 
synthesis  are  much  aided  Avhen  air  is  not  available. 
In  water  plants  those  air  spaces  make  the  plant 
buoyant.  In  the  water  hyacinth,  for  example,  the  large 
air  spaces  in  the  petioles  make  the  plant  so  light  that 
it  floats.  Many  sea  weeds  are  buoyed  up  by  so-called 
air  bladders. 


Questions 

1.  Name  the  parts  of  the  outside  of  a  leaf. 

2.  What  is  the  structure  of  the  inside  of  a  leaf? 

3.  What   arc   stomates?     Where   are  they  found? 
How  numerous  are  they.? 

4.  What  is  the  function  of  stomates? 

5.  What  is  chlorophyll? 

6.  Is  chlorophyll  of  any  importance  to  us? 

7.  What  are  the  raw  materials  used  by  plants  for 
the  manufacture  of  carbohydrates? 

8.  Under  what  conditions  are  these  raw  substances 
combined  to  form  carbohydrates? 

9.  What  is  the  waste  product  in  this  process  ? 

10.  Why  is  this  process  of  so  much  importance  to 
animals? 

11.  In  what  parts  of  plants  is  food  stored? 


218  A  YEAR  IN  SCIENCE 

12.  When  is  this  food  used  by  the  plant? 

13.  Is  this  stored  food  of  any  value  to  us  ?    Explain 
in  what  ways  it  is  of  value. 

14.  How   does   the   composition   of  proteins   differ 
from  that  of  carbohydrates? 

15.  "What  are  solutes? 

16.  Explain    what    is    meant    by    the    process    of 
nutrition. 

17.  Is  it  necessary  for  plants  to  digest  their  food? 

18.  Define  transpiration. 

19.  State  the  disadvantages  of  transpiration. 

20.  State  the  advantages  of  transpiration. 

21.  Describe  the  general  relation  of  plants  to  water. 

22.  .  How  do  plants  living  in  water  differ  from  those 
living  in  a  desert  ? 

23.  What  are  the  principal  ways  in  which  plants  are 
protected  against  loss  of  water  ? 

24.  Is  the  loss   of  leaves   in   the   autumn   of   any 
advantage  to  plants? 

25.  What  causes  the  brilliant  colors  in  leaves  in  the 
autumn  ? 

26.  Why  is  it  necessary  for  plants  to  breathe? 

27.  What   are  the   waste  products  formed  in  the 
process  of  respiration  ?    Where  are  they  given  off  from 
the  plant? 

28.  How  does  the  exchange  of  gases  in  respiration 
in  plants  compare  with  that  in  animals  ? 

29.  Name  plants  in  which  air  is  stored. 


CHAPTER  XXVII 


ROOTS 

Function.  By  roots  we  generally  mean  that  part  of 
the  plant  which  is  underground.  This  position  at  once 
suggests  the  most  obvious  use  of  roots,  that  of  anchor- 
ing the  plant.  The  fact  that  a 
plant  will  not  grow  unless  the  roots 
are  placed  in  suitable  soil,  which 
must  be  kept  moist,  suggests  a 


\S.    87.      .Dandelion  Jb'ig.    88.      Carrot,   a 

showing  a  tap  root.  fleshy  tap  root. 

second     important     function    for     roots;     namely,     to 
absorb  from  the  soil  water    and  substances  iri  solution. 

219 


220 


A  YEAR  IN  SCIENCE 


Structure.  In  many  plants  the 
root  system  contains  one  main  root 
much  longer  than  any  of  its 
branches.  This  is  called  a  tap  root. 
Frequently  food  accumulates  in 
this  main  root  forming  a  fleshy 
tap  root  such  as  the  carrot,  radish, 
dandelion,  beet,  or  turnip.  Some 
plants  have  no  single  main  root, 
but  many  smaller  roots  arising 
from  the  same  point.  These  are 
known  as  fibrous  roots,  examples 
of  which  are  found  in  all  the 
grasses.  Sweet  potatoes  are  thick- 
.ened  fibrous  roots.  The  part  of  the 
root  near  the  stem  may  be  large 
and  stout  and  covered  with  a  thick 
bark.  The  branches,  however, 
gradually  become  smaller,  more 
slender,  and  with  a  thinner  cover- 
ing, or  epidermis.  The  ultimate 

branches  give  rise  to  many  very  delicate  organs,  the 
root  hairs.  When  a  plant  is  pulled  out  of  the  ground, 
the  root  hairs  are  generally  broken  off.  Each  of  these 
very  numerous  hairs  is  an  extremely  thin  walled  tube 
which  opens  into  the  cell  of  the  epidermis  from  which 
it  arises. 

Absorption  of  water  and  solutes.     If  we  recall  the 
amount  of  water  transpired  by  plants,  we  can  form 


Fig:.  89.  Seedling  of 
corn  showing  fibrous 
roots. 


ROOTS 


221 


Fig.  90.  A  length- 
wise section  of  a 
carrot  showing  the 
internal  structure ; 
E,  epidermis ;  C, 
cortex ;  and  W, 
woody  part. 


some  estimate  of  the  amount  of 
water  which  enters  the  roots  of 
E  plants  each  day.  This  absorption 
of  water  takes  place  chiefly  through 
the  root  hairs.  The  soil  water 
contains  all  the  sub- 
stances which  it  can 
dissolve  from  the 
earth  through  which 
it  passes.  This  water 
with  these  solutes 
then  diffuses  through 
the  thin  walls  of  the 
root  hairs.  We  have 
already  learned  that 
some  liquids  will  dif- 
fuse through  an  ani- 
mal membrane  even 
though  there  are  110 
in  the  membrane.  In  exactly  i\& 
as  the  molecules  of  molasses  and 

(See 


.Root  Cap 

Fig.  91.  Radish 
seedling  grown 
in  moist  air  to 
show  the  root 
hairs. 


visible     pores 
same     manner 

water  diffused  through  the  animal  membrane 
Exercise  5),  the  soil  water  and  solutes  pass  through 
the  walls  of  the  root  hairs.  From  there  they  are  con- 
ducted through  tubes  up  through  the  root  into  the  stem. 
Substances  also  pass  out  of  the  roots  into  the  soil. 
Movement  takes  place  in  both  directions  through  the 
walls  of  the  root  hairs.  Those  substances  which  pass 
out  of  the  root  are  waste  products,  excretions. 


222 


A  YEAR  IN  SCIENCE 


It  is  now  known  that  these  substances  are  frequently 
injurious  to  plants.  It  is  probable  that  the  decrease 
in  the  fertility  of  soil  is  frequently  due  to  the  presence 
of  these  excretions  rather  than  to  the  lack  of  the  proper 
mineral  materials.  Most  of  these  excretions  appear 
harmful  to  the  species  of  plants  which  produced  them, 
but  they  are  not  necessarily  so  to  other  plants.  This 
may  help  to  explain  the  benefits  of  rotation  of  crops. 


Fig-.  92.     Soil  is  washed  away  fcy  the  water,  but  large  roots  serve 
as  an  effective  means  of  anchoring  this  tree. 

Anchorage.  Roots  usually  serve  as  a  very  effective 
means  of  holding  plants  in  place.  Many  plants  are 
so  well  anchored  that  during  a  heavy  wind  a  plant 
will  be  broken  off,  but  it  will  not  be  uprooted.  The 


ROOTS  223 

roots  of  ordinary  plants  are  much  larger  than  we 
suppose.  When  a  plant  is  pulled  out  of  the  ground, 
the  larger  part  of  the  root  system  is  broken  off  and 
left  in  the  ground.  The  roots  of  trees  ordinarily  spread 
much  farther  underground  than  their  branches  do  above. 

Roots  seem  to  be  modified  to  suit  their  surroundings. 
However,  we  must  not  fail  to  recognize  the  fact  that 
plants  can  not  adapt  themselves  to  conditions.  In  many 
ways  they  are  very  well  adapted  or  suited  to  the 
conditions  under  which  they  live,  but  that  is  because 
they  are  the  only  plants  which  have  survived.  On 
the  whole,  large  aerial  stem  systems  are  commonly 
associated  with  extensive  root  systems.  The  roots  of 
plants  along  streams  and  shores  are  especially  effective 
for  anchorage.  The  roots  of  these  plants  are  frequently 
matted  together,  thereby  clinging  firmly  to  the  earth. 
As  a  result,  the  water  can  not  wear  away  the  soil  and 
dislodge  the  plant. 

The  size  of  the  root  varies  greatly  with  the  amount 
of  available  water.  The  roots  of  water  and  of  swamp 
plants  are  usually  short.  Those  of  desert  plants,  on  the 
other  hand,  are  often  enormously  developed. 

' '  One  of  the  most  notable  examples  of  an  enormously, 
developed  root  system  is  found  in  the  mesquite  of  the 
far  Southwest  and  Mexico.  When  this  plant  grows  as 
a  shrub,  reaching  the  height,  even  in  old  age,  of  only 
two  or  three  feet,  it  is  because  the  water  supply  in 
the  soil  is  very  scanty.  In  such  cases  the  roots  extend 
down  to  a  depth  of  sixty  feet  or  more,  until  they  reach 


224  A  YEAR  IN  SCIENCE 

water,  and  the  Mexican  farmers  in  digging  wells  follow 
these  roots  as  guides.  Where  water  is  more  abundant, 
the  mesquite  forms  a  good-sized  tree,  with  much 
shorter  roots.''* 


Questions 

1.  State  two  important  functions  of  roots. 

2.  Define  tap  root  and  give  examples. 

3.  What  is  meant  by  fibrous  roots?  Give  examples. 

4.  Describe  root  hairs. 

5.  What  substances  diffuse  into  the  plant  through 
the  root  hairs  ?    What  substances  pass  out  of  the  root  ? 

6.  Do   plant    excretions   have    any    effect    on    the 
fertility  of  soil? 

7.  How  does  the  size  of  the  root  system  of  a  tree 
compare  with  that  of  its  branches? 

8.  How  do  you  account  for  the  fact  that  desert 
plants  have  such  large  root  systems? 

'"'Bergen  and  Davis,  Principles  of  Botany.     Ginn  and  Company. 


CHAPTER  XXVIII 

STEMS 

Functions.  The  main  divisions  of  a  plant  are  the 
root,  stem,  and  leaves.  The  materials  from  which  the 
plant  makes  its  own  food  are  taken  in  through  the 
roots  and  through  the  leaves.  Since  the  leaves  are  the 
factories  in  which  the  food  is  manufactured,  the  raw 
materials,  water  and  solutes,  which  are  taken  in 
through  the  roots,  must  be  transferred  to  them.  In 
return,  some  of  the  food,  after  it  has  been  made,  must 
be  carried  to  the  roots.  This  necessitates  a  transfer 
of  materials  both  to  and  from  the  leaves.  To  make 
starch,  we  already  know,  the  leaf  must  have  light. 
Clearly,  it  would  be  a  decided  disadvantage  to  plants 
if  all  of  their  leaves  were  attached  directly  to  the  roots. 
In  most  plants  an  intermediate  part,  the  stem,  is  present. 
This  connects  the  roots  with  the  leaves  and  thus  forms 
a  passageway  for  the  movement  of  food  and  raw 
materials.  The  chief  function  of  stems,  however,  is  to 
bring  the  leaves  up  into  the  sunlight  where  they  can 
work  to  best  advantage. 

Kinds.  Stems  determine  to  a  great  extent  the  gen- 
eral form  of  plants.  They  often  branch,  and  in  that 
way  increase  their  power  for  displaying  the  leaves  to 

225 


226 


A  YEAR  IN  SCIENCE 


the  light  and  to  the  air.  Stems  exhibit  a  great  variety 
of  form  and  habits.  The  upright,  or  erect  stem,  is  the 
most  common,  and  altogether  seems  to  be  the  best 
device  for  properly  bringing  the  leaves  to  light.  The 
most  conspicuous  erect  stems  are  those  of  trees.  The 
branches  of  erect  stems  usually  have  a  more  or  less 
horizontal  position,  and  are  so  arranged  that  one  does 
not  shade  another.  Hard  tissues  are  always  present 

in  the  large  erect  stems  to  give 
them  support  much  as  bones 
give  support  to  the  bodies  of 
animals. 

In  many  plants  the  stem  lies 
prostrate  on  the  ground,  as  in 
the  strawberry.  Others  have 
developed  a  climbing  habit. 
Such  stems  can  not  stand  alone, 
but  they  have  the  ability  to  sus- 
tain themselves  by  using  sup- 
ports. They  have  various  ways 
of  attaching  themselves  to  the 
supports;  the  ivy  by  means  of 

o1ir,],.jnOi  Hkk«j  •  thp  o-ranp  hv 
sucKing  aibKs  ,  me  grape  uy 

,    .,        ,  , 

tendrils  ;  beans,  morning  glories, 
and  hops  twine  their  stems  about  the  support.  The 
stems  of  desert  plants  are  usually  very  short  and 
thick.  This  is  quite  in  contrast  to  the  enormously 
developed  root  system  of  these  plants.  In  the  cactuses 
the  leaves  are  reduced  to  spines,  and  the  short  thick 


Fig.   93.   Theivy  climbs 
by     means     of     sucking 

disks,  8. 


STEMS  227 

stems  are  green  and  make  the  food  for  the  plants. 
They  also,  you  recall,  store  water. 

Structure.  An  ordinary  stem  is  a  jointed  structure. 
In  some,  such  as  the  corn  stalk  and  the  cane  (used  for 
fishing  rods),  these  joints,  or  nodes,  are  very  evident. 
In  others,  the  joints  are  evident  only  because  they  are 
the  places  where  leaves  and  branches  appear.  If  the 
internal  structure  of  a  stem  is  studied  in  detail,  it  will 
be  found  to  be  very  complex  and  difficult  to  understand. 
We  shall  attempt  to  study  only  such  parts  as  can  be 
seen  with  the  naked  eye.  If  a  twig  of  any  growing 
woody  plant,  such  as  the  box  elder  or  maple,  be  cut 
across,  it  will  be  seen  to  be  made  up  of  four  distinct 
parts:  1.  An  outer  protecting  layer,  the  epidermis. 
2.  A  second  layer  of  soft  tissue,  usually  green, 
the  cortex.  3.  A  layer 
of  wood,  the  vascular 
cylinder.  4.  A  central 
portion,  the  pith.  The 
cortex  when  green  is 
able  to  manufacture  car- 
bohydrates just  as  the 
leaves  do.  The  wood  is 
the  conducting  region, 
and  it  also  gives  strengthFig.  94.  Cross  section  of  a  three-year- 

,     .    .  ,.,  ,,  old  woody  stem. 

and  rigidity  to  the  stem. 

If  examined  more  closely  this  section  of  wood  will  be 
seen  to  be  divided  into  a  number  of  segments  by  plates 
of  cells  passing  from  the  pith  to  the  cortex.  These 


228 


A  YEAR  IN  SCIENCE 


are  known  as  pith,  or  medullary  rays.  The  wood  itself 
is  made  of  bundles  of  tubes  known  as  vascular  bundles. 
Some  of  the  tubes  in  each  bundle  are  used  for  con- 
ducting water  from  the  root  to  the  leaves,  and  others 
for  conducting  prepared  food  materials  downward. 


Cortex 

Vascular 
Cylinder 


Pith 


Fibrovascular 
Bundle 


Cambium 


Fig.   95.     Cross  section  of  a  woody  stem   showing  details   of 
structure. 

If  a  cross  section  of  a  young  stem  were  examined 
under  a  microscope,  a  region  of  thin-walled,  rectangular- 
shaped  cells  would  be  found  between  the  wood  and 
bark  regions.  This  is  the  growing  region  of  the  stem 


STEMS 


229 


and  is  called  the  cambium  layer.  It  is  in  this  layer  that 
the  new  cells  which  make  the  new  wood  and  bark  are 
formed. 

Steins  of  this  type  can  increase  in  diameter.  A  new 
layer  of  wood  is  formed  outside  of  the  old  wood. 
Usually  these  layers  of  wood  are  so  distinct  that  a 
section  of  a  woody  stem  shows  a  series  of  concentric 
rings,  usually  one  ring  for  each  year.  If  a  three  or 
four  year  old  twi«-  is  examined,  several  changes  which 
take  place  as  stems  grow  older  will  be  noted.  A  thicker 
covering  composed  of  waterproof  bark  is  present. 
The  wood  cylinder  will  be  found  to  be  much  larger, 
and  the  pith,  smaller.  In  the  stems  of  some  plants, 
such  as  lilies,  grasses,  and  palms,  the  vascular  bundles 


Pith 


Rind 


Fibrovascular 
Bundle 


Fig.  96.     Cross  section  of  a  corn  stem  showing  the  vascular  bundles 
scattered  in  the  pith. 


230 


A  YEAR  IN  SCIENCE 


are  not  arranged  in  the  form  of  a  hollow  cylinder, 
but  are  more  or  less  irregularly  scattered  through 
the  pith.  In  these  stems  each  vascular  bundle  has  its 
own  cambium  layer. 

If  the  cut  ends  of  any  young  branches  are  placed 
in  red  ink  (a  solution  of  eosin)  and  left  in  the  sunlight 
for  a  few  hours  and  then  examined,  the  red  ink  will 
be  found  to  have  passed  up  the  stem.  In  sections  of 
such  stems  the  color  wilLbe  found  in  the  woody  tubes 
just  beneath  the  bark.  This  color 
indicates  the  path  taken  by  the 
ascending  water.  The  liquids  in 
trees  abandon  the  inner  older  wood 
and  move  only  through  the  newer 
wood.  This  older  wood  forms  the 
heart  wood. 

Liquids    entering    through    the 
root  hairs  pass  into  tubes  in  the 
roots.      These    tubes    are    continu- 
ous with  those  in  the  wood  of  the 
Fig.  97.    Longitudi-     stem,  which  in  turn  join  those  in 

nal  section   of  a  stem       Jl  ...       ..       , 

showing  the  path  taken     the  veins  in  the  leaves,  thus  lorm- 

by  ascending  water. 

ing  a  continuous  passageway  from 
the  root  hairs  to  the  leaves. 


Questions 

1.  What  is  the  principal  function  of  stems? 

2.  What  plants  have  stems  which  stand  erect? 

3.  Name   plants  which  have  the   climbing  habit. 


STEMS  231 

What  are  some  of  the  ways  by  which  they  attach  them- 
selves to  their  supports? 

4.  Describe    the    internal   structure    of    a    woody 
stem. 

5.  What  are  vascular  bundles?     What  are  their 
functions? 

6.  How  do  trees  increase  in  diameter? 

7.  What  forms  the  grain  in  woods? 

8.  Describe  the  way  in  which  the  vascular  bundles 
in  a  corn  stem  are  arranged. 

9.  What  is  the  path  taken  by  liquids  as  they  pass 
from  the  roots  of  plants  to  the  leaves? 

10.     Where  do  liquids  travel  in  passing  from  the  leaves 
to  the  roots? 


CHAPTER  XXIX 

REPRODUCTION 

Reproduction  and  nutrition.  By  means  of  roots, 
stems,  and  leaves,  as  we  have  just  learned,  plants  arc 
able  to  carry  on  certain  processes  by  which  they  live. 
These  processes  of  nutrition  are  necessary  for  the  life 
of  any  individual  plant.  It  is  also  essential,  however, 
for  new  and  younger  plants  to  be  produced ;  otherwise 
each  particular  kind  (species)  of  plant  would  cease  to 
exist  on  earth.  This  function  of  producing  new  plants 
is  known  as  reproduction  (to  produce  again).  There 
are  a  number  of  methods  by  Avhich  new  plants  may 
arise  from  old  ones.  It  is  possible  to  take  cuttings 
of  willow,  or  geranium,  or  grape,  plant  them,  and 
have  them  grow  into  new  plants.  In  all  the  higher, 
so-called  seed  or  flowering  plants,  seeds  are  used  for 
the  production  of  new  plants.  For  the  formation  of 
seeds  plants  bear  special  structures,  the  flowers. 

Flowers.  Most  of  the  plants,  with  wrhich  you  arc 
familiar,  periodically  produce  highly  colored  structures 
which  are  called  flowers.  The  size,  shape,  color,  and 
even  the  structure  of  flowers  of  different  plants  vary 
greatly.  In  any  simple  flower,  such  as  the  trillium, 
the  violet,  or  the  geranium,  four  parts  are  always  present. 

232 


REPRODUCTION* 


233 


Petal 


Pist 


Sepal 


Starnen 


Fig.  98.     Flower  of  a  tulip. 

1.  The  outermost  part  is  the  tY////.r,  which  is  green.  It  is 
composed  of  separate  parts,  the  sepals.  2.  Inside  and 
above  the  calyx  is  the  corolla,  usually  the  most  conspicu- 


Petal 


Receptacle 
Fig.    99.      Diagram   of  a  section  of  a  tulip  flower. 


234 


A  YEAR  IN  SCIENCE 


ous  part  of  a  flower  because  of  its  bright  color.  The 
corolla  is  made  up  of  leaf -like  parts  called  petals.  3,  Just 
within  the"  corolla  are  a  number  of  slender  structures, 
the  stamens.  Each  stamen  has  a  slender  stalk,  the 
filament,  the  end  of  which  is  enlarged  to  form  the 
anther.  Within  the  anther  is  a  powder-like  substance 
called  pollen.  4.  In  the  center  of  the  flower  is  the 
pistil.  The  swollen  base  of  the  pistil  is  the  ovary. 
Above  this  is  a  slender  stalk,  the  style,  at  the  top  of 


Pistil 


Fig.  100.     Section  of  a  flower  of  a  hyacinth. 

which  is  an  expanded,  often  branched  structure,  the 
stigma.  In  the  ovary  are  the  ovules  which  under  cer- 
tain conditions  develop  into  seeds. 

Formation  of  seeds.  Only  two  parts  of  a  flower,  the 
ovule  and  pollen,  are  necessary  to  form  a  seed.  If 
we  examine  a  very  thin  section  of  an  ovule  under  a 


REPRODUCTION 


235 


microscope,  we  find  that  in  the  center  of  it  there  is  an 
elongated  sac  known  as  the  embryo  sew.  This  contains 
protoplasm  and  several  nuclei.  One  of  these  nuclei, 
together  with  the  protoplasm  immediately  around  it, 
forms  the  egg  cell.  The  pollen  grains  are  formed  in 
the  anther  of  the  stamen.  When  the  anther  breaks 
open  these  small  cells  are  scattered  and  some  fall  upon 
the  stigma.  Changes  then  take  place  in  the  pollen 
grain  and  as  a  result  a  tube,  the  pollen  tube,  develops. 
This  tube  continues  to  grow  downward  through  the 
stigma  and  style.  It  enters  the  ovule  and  grows  toward 
the  egg.  During  this  time  two  cells,  sperm  cells,  have 


From   Caldwell  and   Eikenberry's   "Elements   of   General   Science," 
by  permission  of  Ginn  and  Company,  Publishers. 

Fig.  101.  Diagram  to  show  development  of  young  plant  from 
the  egg.  A,  entire  pistil ;  B  and  C,  development  of  seed  ;  D,  seed- 
ling plant ;  pol.,  pollen  grain ;  p.  t.,  pollen  tube ;  ov.,  ovule ;  sac, 
embryo  sac ;  emb.,  embryo ;  sd.}  mature  seed. 

developed  in  the  pollen  tube.  One  of  these  sperm 
cells  may  unite  with  the  egg  cell  and  form  a  single 
cell.  This  process  is  known  as  fertilization.  After 
fertilization  this  egg  begins  to  divide  and  to  form  the 
new  plant.  One  region  develops  into  the  root  tip, 


236  A  YEAR  IN  SCIENCE 

another  into  a  stem  tip,  and  others  into  one  or  more 
leaves.  After  the  embryo  plant  reaches  this  stage,  in 
most  cases,  the  wall  of  the  ovule  becomes  hardened  and 
the  growth  of  the  young  plant  is  checked.  This  ovule 
with  the  thickened  wall  and  containing  a  plant  in  a 
dormant  condition  is  a  seed.  It  may  lie  in  this  con- 
dition for  a  long  time  and  then  if  placed  under 
favorable  conditions,  the  seed  coat  will  burst  and  the 
embryo  plant  will  continue  its  growth  into  a  young 
plant. 

Pollination.  Pollen  is  necessary  for  the  production 
of  seeds.  But  before  this  pollen  can  fertilize  an  ovule, 
it  must  first  be  transferred  from  the  anther  in  which 
it  is  formed  to  a  stigma.  This  transfer  of  pollen  from 
anther  to.  stigma  is  called  pollination.  This  process 
appears  to  be  one  of  the  chief  activities  associated  with 
flowers.  There  are  two  kinds  of  pollination.  Pollen 
may  be  transferred  from  the  anther  to  the  stigma  of 
the  sapie  flower  (self  pollination),  or  to  the  stigmas  of 
other  flowers  (cross  pollination).  Charles  Darwin,  the 
great  English  naturalist,  found,  about  the  middle  of 
the  nineteenth  century,  that  certain  kinds  of  flowers 
were  entirely  dependent  for  fertilization  upon  cross 
pollination.  He  also  found  that  some  which  were  self 
pollinated  did  not  produce  so  many  seeds,  and  that 
plants  which  grew  from  those  seeds  were  smaller  and 
weaker  than  plants  from  seeds  produced  by  cross 
pollinated  flowers.  He  also  found  that  another 
advantage  of  cross  pollination  was  that  the  plants  so 


REPRODUCTION  237 

produced  varied  more  than  those  which  came  from  self 
pollinated  seeds. 

In  many  plants,  however,  self  pollination  occurs. 
Sometimes  this  is  accidental,  but  in  many  flowers  self 
pollination  is  apparently  definitely  provided  for.  The 
positions  of  the  anthers  and  the  stigmas  are  often  such 
that  some  of  the  pollen  must  fall  directly  upon  the 
stigma.  Some  plants,  like  the  closed  gentian,  produce 
flowers  which  never  open  and  are  thus  necessarily 
self-pollinated.  Cross  pollination  is  the  more  common 
method,  and  there  are  various  devices  for  securing  it. 
In  some  species  of  plants  the  flowers  do  not  have  both 
ovaries  and  stamens.  The  flowers  on  some  plants  have 
only  ovaries,  while  those  on  other  plants  of  the  same 
species  have  only  stamens.  In  other  species  the  stamens 
and  ovaries  of  the  same  flower  do  not  mature  at  the 
same  time.  Cross  pollination  is  usually  secured  through 
one  of  two  agencies,  the  wind  or  insects.  Flowers  which 
depend  upon  insects  for  cross  fertilization  are  made 
attractive.  Their  showy  color,  their  odor,  and  the 
nectar  which  they  contain,  all  serve  as  attractive  fea- 
tures for  insects.  The  pollen  is  used  by  many  for  food. 
Xectar  is  also  used  for  food  and  out  of  it  the  bee  makes 
honey.  Flowers  are  visited  by  a  great  many  kinds  of 
insects.  Those  which  are  most  useful  for  transferring 
pollen  have  bodies  covered  with  hairs  to  which  the 
pollen  easily  adheres.  In  the  bee  a  certain  part  of  the 
hind  leg  is  covered  with  stiff  hairs  forming  a  "pollen 
basket."  The  bee  collects  pollen  for  food,  but  while 


238 


A  YEAR  IN  SCIENCE 


getting  it  for  itself,  pollen  is  caught  on  the  hairs  of  the 
body  and  legs  of  the  bee  and  is  thus  carried  from  flower 
to  flower.  Bees,  butterflies,  moths,  and  some  other 
insects  feed  on  the  nectar  of  plants.  These  insects 
have  mouth  parts  Avhich  are  very  much  elongated, 
forming  a  tube-like  structure.  This  enables  them  to 
reach  the  nectar  which  is  usually  at  the  base  of  the 
flower.  In  so  doing,  however,  the  body  of  the  insect 
must  brush  against  the  stamens  and  pistils.  In  this 
manner  pollen  is  then  transferred  from  one  flower  to 
another. 

Wind  pollinated  flowers  aTe  usually  very  inconspicu- 
ous. They  are  structures  which  you  probably  have 
never  considered  flowers  at  all.  The  flowers  of  most 
trees,  grasses,  and  grains  are  wind  pollinated. 

Seed  dispersal.  The 
function  of  the  seed 
is  to  produce  a  new 
plant.  In  order  to  do 
this,  however,  certain 
conditions  of  light, 
air,  moisture,  and 
food  are  necessary. 
Only  a  small  propor- 
tion of  the  seeds  an- 
nually produced  can 
grow.  This  is  be- 
cause a  seed  must  not  only -have  favorable  conditions  of 
light,  moisture,  etc.,  for  growth,  but  it  must  find  a  place 


Fig.    102.      Milk    weed    fruit,    showing 
method  of  seed  dispersal. 


REPRODUCTION 


239 


where  there  are  not  too  many  other  plants  wanting  these 
same  conditions.  If  all  the  seeds  formed  dropped  about 
the  parent  plant,  and  developed  into  plants,  there  would 
soon  be  so  many  of  them  that  they  would  seriously  inter- 
fere with  one  another.  It  is  thus  of  great  advantage  to 
plants  to  have  the  seeds  widely  scattered  so  that  some 
may  find  all  the  conditions  favorable  to  growth. 

There  are  many  methods  by  which  seeds  are  widely 
scattered.     Many  seeds  and  fruits  are  so  constructed 


Maple 


Elm 


Fig.  103.     Group  of  winged  fruits. 

that  they  are  very  likely  to  be  carried  about  by  wind, 
water,  or  animals.  You  can  easily  think  of  many  seeds 
and  fruits  dispersed  by  each  of  these  agents.  Think 
of  the  winged  fruits  of  the  maples,  elms,  or  catalpas 
which  are  so  easily  carried  by  the  ^vvind.  So,  too,  are 
the  tufted  seed-like  fruits  of  the  thistle,  dandelion,  and 
milk  weed.  Various  burrs,  Spanish  needles,  and  beggar 


240 


A  YEAR  IN  SCIENCE 


Cockleburr  Beggar's-tick 

Fig.  105.     Some  fruits  which  are 
carried  by  animals. 

ticks  have  hooks,  or  spines,  which 
enable  them  to  cling  to  the  hair,  fur, 
or  feathers  of  animals.  They  may  be 
carried  many  miles  before  they  are 
brushed  off.  Sometimes  seeds  or 
fruits  may  fall  into  water.  Such  seeds  are  buoyant  and 
are  frequently  carried  many  miles  before  they  are 
deposited. 


Fig.  104.     Fruits  of 
dandelion. 


Questions 

1.  By  what  .methods  may  new  plants  arise  from 
old  ones?     Give  examples  of  plants  illustrating  each 
of  these  -methods. 

2.  What  is  the  function  of  a  flower? 

3.  Describe  the  structure  of  a  typical  flower. 

4.  Which  parts  of  a  flower  are  necessary  to  form 
a  seed? 

5.  What  is  an  egg  cell?    A  sperm  cell? 

6.  Define  fertilization. 

7.  How  is  a  seed  formed? 

8.  Define  pollination. 

9.  Discuss  the  twro  kinds  of  pollination. 

10.  What  are  the  principal  agencies  by  means  of 
which  cross  pollination  is  accomplished  ? 

11.  Name  flowers  which  are  wind  pollinated. 


REPRODUCTIOX  241 

12.  Name  flowers  which  are  pollinated  by  insects. 

13.  What  is  the  function  of  a  seed? 

14.  Of  what  advantage  is  seed  dispersal  to  a  plant? 

15.  What    are    the    conditions    necessary    for    the 
germination  of  seeds? 

16.  Give  examples  of  seeds  dispersed  by  wind.  How 
does  the  structure  of  these  seeds  favor  such  dispersal? 

17.  Discuss  the  value  of  water  as  an  agency  for  seed 
dispersal. 

18.  Givre    examples   of   seeds   carried   by   animals. 
How  does  their  structure  adapt  them  for  this  method 
of  dispersal? 

19.  Discuss  the  ways  in  which  seeds  are  of  importance 
to  man. 

20.  What  conditions  are  necessary  for  the  growth  of 
seeds  ? 

21.  Discuss  the  vitality  of  seeds. 


CHAPTER  XXX 

IMPORTANCE  OF  PLANTS  TO  MAN 

Economic  importance.  Plants  are  of  great  economic 
importance  to  man.  Some  of  them  are  important 
because  they  are  beneficial;  others,  because  they  are 
injurious.  As  to  benefits:  they  supply  man  "with  his 
cereals  and  flour,  his  fruits  and  garden  vegetables,  his 
nuts  and  spices,  his  beverages  and  the  sugar  to  sweeten 
them,  his  medicines  and  his  dyestuffs;  they  supply 
the  material  out  of  which  many  of  his  clothes  are  made, 
the  thread  with  which  they  are  sewed  together,  the 
paper  which  covers  the  packages  in  which  they  are 
delivered,  and  the  string  with  which  the  package  is  tied. 
The  various  uses  of  the  forest  have  been  mentioned 
before;  the  need  of  trees  to  protect  the  earth,  their 
usefulness  in  the  holding  of  the  water  supply,  their 
direct  economic  importance  for  lumber  and  firewood. 
Many  of  us  forget,  too,  that  much  of  the  energy 
released  on  this  earth  to  man,  as  heat,  light,  or  motive 
power,  comes  from  the  dead  and  compressed  bodies  of 
plants  which  thousands  of  years  ago  lived  on  the  earth 
and  now  form  coal.  Plants  are  thus  seen  to  be  of 
immense  direct  economic  importance  to  mankind."* 

*Hunter,  Essentials  of  Biology.     American  Book  Company. 

242 


IMPORTANCE  OF  PLANTS  TO  MAN 


243 


Those  plants  which  are  the  most  harmful  to  man 
belong  to  a  group  of  plants  known  as  fungi.  Many 
diseases  of  cultivated  crops,  of  farm  animals,  and  of 
man  himself  are  caused  by  members  of  this  group. 
The  plants  which  belong  to  the  fungi  do  not  have 
chlorophyll.  Consequently  they  are  unable  to  make 
their  own  food  and  must  depend  upon  other  living 
organisms  for  securing  it.  Some  of  them  obtain  their 
food  directly  from  living  plants  or  animals  and  are 
called  parasites.  The  plant  or  animal  from  which  they 
derive  their  food  is  called  the  host.  The  parasite  attaches 
itself  to  its  host  and  sucks  out  its  food  supply.  Others 
use  non-living  substances  for  food,  but  these  substances 
were  once  a  part  of  living  organisms.  These  are  called 
saprophytes.  Yeasts,  molds,  mushrooms,  and  bacteria 
are  fungi.  Of  these,  bacteria  have  by  far  the  greatest 
economic  importance. 


Fig.  106.     A  mold  which  forms  a  white  furry  growth  on  damp  bread. 

Bacteria.    The  study  of  bacteria  is  a  special  subject 
called  bacteriology.     This  fact  in  itself  indicates  some- 


244 


A  YEAR  IN  SCIENCE 


thing   of  the   importance   attached   to   this   group   of 

• 

plants.  Bacteria  are  the  smallest  living  organisms. 
They  can  be  seen  only  with  the  very  highest  powers  of 
the  microscope;  there  are  reasons  for  believing  that 
there  are  bacteria  too  small  to  be  seen  even  with  the 
best  microscope.  They  are  sometimes  not  over  1/50,000 
inch  in  diameter,  and  even  the  largest  ones  are  not 
more  than  1/10,000  inch  in  diameter.  In  structure  they 
are  very  simple,  consisting  of  but  a  single  cell,  and 
little  is  known  about  them  except  their  general  external 
appearance.  Usually  three  groups  of  bacteria  are 
recognized.  These  are  classed  according  to  form:  the 

spherical  (coccus),  rod- 
like  (bacillus),  and 
spiral  (spirillum).  Many 
kinds  of  bacteria  are  en- 
dowed with  the  power  of 
motion.  The  locomotive 
organs  consist  of  minute 
hair-like  bodies  which 
project  from  the  bodies 


^ 


Fig.  107.  A  group  of  various 
kinds  of  bacteria  ;  A,  coccus  forms  ; 
B,  spirillum  forms  ;  and  C,  bacillus 
forms. 


of  the  bacteria.  These 
little  hairs,  called  flag- 
ella,  wave  back  and 
forth  and  by  this  mo- 
tion drive  the  bacteria  through  the  water. 

Bacteria  are  found  everywhere  in  the  earth,  in  the 
water,  and  in  the  air.  They  live  upon  any  kind  of 
organic  material  and  under  conditions  which  would  kill 


IMPORTANCE  OF  PLANTS  TO  MAN  245 

all  other  organisms.  Some  bacteria  can  live  even  with- 
out free  oxygen.  They  multiply  very  rapidly  by  simple 
division.  An  adult  individual  may  divide  into  two,  each 
of  these  into  two,  and  so  on.  The  rapidity  with  which 
they  multiply  is  almost  inconceivable.  It  has  been 
estimated  that  a  single  individual  will  produce  about 
17,000,000  offspring  in  twenty-four  hours. 

Conditions  for  growth  of  bacteria.  Like  other  living 
things,  bacteria  will  not  grow  at  freezing  temperature 
or  below.  They  will  grow  at  nearly  all  tem- 
peratures above  freezing,  some  species  even  growing 
at  140°  F.  Most  bacteria  are  killed  by  excessive  heat, 
and  usually  a  temperature  of  from  149°  F.  to  160°  F.,  if 
continued  for  an  hour,  is  sufficient  to  destroy  them. 
When  the  bacteria  in  a  substance  are  destroyed^  the 
substance  is  said  to  be  sterilized.  A  low  temperature 
may  not  kill  them,  but  it  does  prevent  their  rapid 
development.  Most  bacteria  need  plenty  of  air  and 
plenty  of  water.  Fortunately  direct  sunlight  kills 
them,  and  this  fact  suggests  a  possible  advantage  in 
having  plenty  of  sunshine  in  our  houses. 

Bacteria  and  disease.  Many  diseases  of  plants  and 
animals  are  produced  by  bacteria.  By  far  the  most 
important  of  the  disease-producing  bacteria  are  those 
which  may  be  parasitic  in  the  human  body  and  cause 
such  diseases  as  tuberculosis,  pneumonia,  cholera, 
typhoid  fever,  diphtheria,  leprosy,  lockjaw,  and  many 
others.  These  bacteria  are  frequently  transferred  from 
one  person  to  another.  A  disease  which  can  be  spread 


246  A  YEAR  IN  (SCIENCE 

in  this  way  is  said  to  be  infectious.  We  are  just 
beginning  to  realize  how  essential  it  is  to  use  all  pos- 
sible precaution  to  prevent  the  spread  of  diseases.  Tlie 
modern  tendency  in  medicine  is  to  determine  how  to 
prevent  diseases,  rather  than  how  to  cure  them. 

Decay.  If  any  organic  substance  is  moist,  bacteria 
will  get  into  it  from  some  source.  They  will  grow 
rapidly  and  in  a  few  hours  marked  changes  will  appear 
in  the  substance.  The  essential  effect  which  the  bac- 
teria produce  is  the  chemical  decomposition  of  the 
material  upon  which  they  are  feeding.  Some  of  the 
simple  substances  formed  by  such  decomposition  are 
consumed  by  the  bacteria;  others  are  not,  and 
are  left  behind  but  not  in  the  form  of  the  original 
substance.  This  process  of  decomposition,  brought 
about  by  bacteria  is  called  decay.  As  a  result  of  it, 
meats  become  putrid,  eggs  rot,  milk  sours,  and  fruits 
spoil.  Decay  is  not  ahvays  harmful.  It  is  in  some 
Avays  of  the  utmost  value  to  man.  By  means  of  it  the 
dead  bodies  of  animals  and  plants  and  the  waste 
products  of  living  ones  are  decomposed  and  reduced 
to  a  form  in  which  they  can  be  removed.  The  materials 
that  are  broken  down  are  thus  made  usable  and  avail- 
able for  the  growth  of  other  plants  and  animals.  Decay 
is  essential  for  life.  Without  it,  all  food  would  finally 
be  unavailable  because  it  would  be  "locked  up"  in  the 
bodies  of  plants  and  animals. 

To  prevent  the  decay  of  food  substances  useful  to 
man,  it  is  necessary  to  destroy  the  bacteria  in  them, 


IMPORTANCE  OF  PLANTS  TO  MAN  247 

or  to  prevent  their  further  growth.  This  may  be  done 
in  several  ways.  The  methods  most  commonly  employed 
for  killing  them  are  boiling  or  using  chemicals  called 
preservatives.  The  former  method  is  the  better 
because  chemicals  which  will  destroy  bacteria  are 
likely  to  be  poisonous  to  man,  and  therefore  should 
not  be  used  in  his  food.  Preservatives  frequently  used 
are  formaldehyde,  borax,  boracic  acid,  and  salicylic 
acid.  In  canning  fruits  and  other  foods  heat  is  used. 
The  fruit  is  first  boiled  to  kill  all  bacteria  in  it.  The 
can  is  sterilized  by  putting  it  in  boiling  water,  and 
then  the  fruit  is  sealed  in*  it  air-tight  while  still  hot. 
If  this  process  has  been  carefully  done,  there  will  then 
be  no  bacteria  in  the  can  and  none  can  enter. 

Other  methods  for  preserving  foods  are  keeping 
them  cold  (refrigeration),  drying,  smoking, 'or  using 
salt,  sugar,  or  vinegar. 

Useful  bacteria.  The  injury  done  by  bacteria  is  so 
very  apparent  that  we  sometimes  overlook  the  fact 
that  many  bacteria  are  of  benefit  to  man.  Mention 
has  already  been  made  of  their  value  in  causing  decay, 
and  in  enriching  the  soil  by  adding  nitrogen  compounds 
to  it  (see  page  122).  Bacteria  are  also  useful  in  the 
production  of  several  foods.  Vinegar,  for  example,  is 
formed  as  a  result  of  their  action  upon  the  fruit  juice, 
cider.  The  flavor  of  butter  is  partly  due  to  bacteria, 
and  that  of  cheese  is  almost  entirely  the  result  of  the 
kinds  of  bacteria  used  in  "ripening"  it. 


248  A  YEAR  IN  SCIENCE 

Questions 

1.  Name  ten  plants  of  economic  value. 

2.  In  what  way  is  each  of  these  plants  useful  to 
man? 

3.  What  is  the  name  of  the  group  of  plants  which 
include  those  most  harmful  to  man? 

4.  Give  three  examples  of  plants  belonging  to  this 
group. 

5.  Define  parasite,  saprophyte,  and  host. 

6.  Where  are  bacteria  found  ?    What  is  their  size  ? 
How  do  they  multiply? 

7.  What    conditions    are    most    favorable    to    the 
growth  of  bacteria? 

8.  When  is  a  substance  said  to  be  sterilized? 

9.  Is  there  any  advantage  in  having  plenty  of  sun- 
shine in  our  houses? 

10.  Name  diseases  which  are  produced  by  bacteria. 

11.  WThat  are  infectious  diseases? 

12.  Why  is  it  important  to  know  whether  or  not  a 
disease  is  infectious? 

13.  Discuss  the  relation  of  bacteria  to  decay. 

14.  State  the  ways  in  which  decay  is  of  value  to 
man. 

15.  What  are  the  chief  methods  used  to  preserve 
our  foods? 

16.  What  are  the  objections  to  the  vise  of  preserva- 
tives in  foods? 

17.  Discuss    the    ways    in    which    bacteria    are    of 
benefit  to  man. 


CHAPTER  XXXI 
ANIMALS 

Distribution.  Animals  are  found  wherever  the  con- 
ditions are  suitable  for  their  existence.  The  chief 
external  conditions  which  influence  animal  life  are 
food,  oxygen,  moisture,  and  suitable  temperature. 
There  are  only  a  few"  places  where  these  conditions 
are  not  favorable  to  the  life  of  some  kind  of  animals. 
In  an  ice  covered  region,  like  the  interior  of  Green- 
land, and  in  exceedingly  dry  areas,  like  the  Sahara 
and  other  deserts,  there  is  almost  no  life  of  any  kind. 
With  a  few  exceptions  like  these,  animals  exist  every- 
where in  great  numbers  and  in  great  variety.  The 
animal  life  of  any  region  is  known  as  its  fauna. 

From  personal  knowledge  most  of  us  are  already 
familiar  with  the  fact  that  animals  differ  very  greatly 
irrespective  of  their  living  places  on  the  surface  of 
the  earth.  We  know  that  the  animals  in  our  immediate 
locality  are  unlike.  The  animals  which  are  found  in 
the  ponds  and  streams  differ  from  those  of  the  prairie ; 
those  of  the  field  differ  from  those  of  the  forest.  The 
greatest  differences  exist  between  the  animals  which 
live  in  water  and  those  which  live  on  land.  These 

249 


250  A  YEAR  IN  SCIENCE 

differences  result  primarily  from  the  methods  of  breath- 
ing. These  two  groups  can  again  be  divided  into  the 
fresh  and  the  salt  water  forms,  and  into  the  land  and 
aerial  forms. 

Means  of  distribution.  Animals  are  distributed  in 
many  ways.  The  chief  method  for  their  dispersal  is 
by  means  of  their  own  powers  of  locomotion.  They 
wander  about  to  search  for  food,  to  escape  drouth  or  a 
sudden  change  of  temperature,  or  sometimes  to  escape 
an  advancing  enemy.  Water  forms  are  carried  about 
by  waves  and  currents.  Some  smaller  animals  are 
transferred  on  the  bodies  of  larger  ones.  Many  have 
been  transferred  from  one  place  to  another  by  man.  In 
several  instances  this  has  proved  a  great  disadvantage 
to  him.  The  English  sparrow,  for  example,  was  intro- 
duced into  this  country  by  man.  It  has  been  able  to 
thrive  here  to  such  an  extent  that  it  has  become  a 
pest  because  of  its  great  numbers  and  because  it  feeds 
on  grains,  seeds,  and  fruits.  The  gypsy  moth  was 
accidentally  introduced  into  the  United  States  by  man. 
More  than  a  million  dollars  are  now  being  spent  each 
year  trying  to  control  this  pest  and  to  protect  the  trees 
of  Northeastern  United  States. 

Factors  determining  distribution.  Every  kind  of 
animal  multiplies  and  spreads  from  a  given  location.  It 
would  ultimately  be  found  all  over  the  surface  of  the 
earth  where  conditions  suitable  for  its  maintenance 
exist  except  for  three  factors  which  prevent  this  uniform 
distribution : 


ANIMALS  251 

1.  Barriers  of  some  sort,  as  mountains  and  oceans, 
may  prevent  a  given  species  of  animal  from  reaching 
certain  regions. 

2.  The  species  may  reach  another  region,  but  when 
there,  it  may  be  unable  to  maintain  itself. 

3.  It  may  maintain  itself,  but  in  so  doing  it  may 
become  so  changed  that  it  will  form  a  new  species. 

Barriers  to  distribution.  It  is  very  evident  that  cer- 
tain conditions  will  prevent  the  spread  of  animals. 
Land  forms,  for  example,  can  not  live  in  water;  and 
salt  water  forms  can  not  live  in  fresh  water.  Animals 
are  prevented  from  reaching  certain  parts  of  the  earth 
by  mountains,  "by  rivers,  by  oceans,  by  deserts,  and, 
sometimes,  by  falls  in  rivers.  There  is  no  evident  reason 
why  the  lion  and  tiger  could  not  live  in  South  America 
or  coyotes  in  Europe,  or  certain  birds,  as  the  meadow 
lark,  in  Europe,  if  it  were  not  for  the  fact  that  they 
have  been  prevented  from  reaching  those  places  by 
natural  barriers. 

Animals  can  not  maintain  their  ground.  Polar  bears 
if  introduced  into  the  tropics  could  not  adjust  them- 
selves to  conditions  so  as  to  live.  Likewise,  tropical 
animals  could  not  survive  the  cold  winters  of  temperate 
regions. 

Sometimes  animals  have  been  introduced  into  regions 
where  the  conditions  were  very  little  changed,  and  yet 
they  were  not  able  to  survive.  This  was  probably 
because  of  competition  with  animals  already  present 
in  the  new  region. 


252 


A  YEAR  IN  SCIENCE 


Change  due  to  new  conditions.  New  conditions  may 
so  alter  a  species  of  animal  that  it  no  longer  exactly 
resembles  the  form  from  Avhich  it  came.  For  example, 
animals  sometimes  adapt  themselves  to  caves.  As  a 
result  they  become  blind  and  lose  their  color. 

Adaptation.  There  are  so  many  animals,  and  conse- 
quently so  much  strife  for  a  place  in  this  crowd,  that 
all  animals  must  adjust  themselves  to  conditions  in 
order  to  survive.  If  they  can  not  change  so  as  to  be 
fitted  for  given  conditions,  they  die.  We  have  already 


of  Field  Museum  of  Natural  History. 
Fig.  108.     The  polar  bear  is  adapted  for  life  in  the  Arctic  regions. 


noted  the  inability  of  a  polar  bear  to  live  in  a  warm 
climate. 

All  animals  are  more  or  less  fitted,  or  adapted,  to 
their  environment  and  to  the  kind  of  life  which  they 


ANIMALS  253 

must  lead.  Some  animals,  such  as  the  vulture,  are  pro- 
vided with  strong  claws  to  aid  in  securing  food;  the 
long  neck  of  the  giraffe  enables  it  to  feed  on  the  foliage 
of  the  trees.  Special  weapons  of  defense  are  found  in 
many  animals,  such  as  the  horns  of  a  cow,  the  sting 
of  the  bee,  or  the  quills  of  the  porcupine.  Insects  are 
frequently  colored  like  their  surroundings  to  escape 
detection.  Animals  like  the  moles,  which 'live  under- 
ground, have  the  legs  modified  for  digging  or  burrow- 
ing. Even  beginners  in  the  study  of  animals  can  find 
many  examples  of  adaptation  in  the  forms  of  life  about 
them. 


Questions 

1.  Name  the  animals  found  in  the  region  in  which 
you  live. 

2.  Are  animals  uniformly  distributed  over  the  sur- 
face of  the  earth? 

3.  Discuss  the  chief  factors  which  determine  the 
distribution  of  animals. 

4.  What  is  meant  by  adaptation?    Give  examples 
of  adaptations  found  in  animals. 


CHAPTER  XXXII 


GROUPS  OF  ANIMALS 

General  statement.  Most  animals  which  arc  known 
to  man  have  been  classified.  By  this  we  mean  that 
they  have  been  placed  in  groups  with  animals  which 

resemble  one  another. 
It  is  interesting,  even 
to  a  beginner,  to  know 
"something  about  the 
groups  of  animals 
and  the  forms  which 
belong  to  the  different 
groups. 

In  some  animals, 
such  as  the  fish  or 
bird,  there  is  a  sup- 
porting frame  work 
in  the  body  made  of 
bone.  This  is  the 

skeleton.     A  part  of 
Fit  109.     Skeleton  of  a  pigeon.        .    ^  ^^  forms  & 

structure  known  as  the  back  bone  or  vertebral  column. 
All  animals  having  a  vertebral  column  are  placed 
together  in  one  group,  the  vertebrates.  Other  animals, 

254 


GROUPS  OF  ANIMALS 


255 


such  as  worms  and  insects,  do  not  have  a  back  bone  and 
are  known  as  the  invertebrates.  To  the  vertebrates 
belong  most  of  the  animals  with  which  you  are  already 


Fig.  110.     The  backbone  of  a  snake  is  composed  of  many  vertebrae. 

familiar  from  personal  observations.  You,  perhaps,  have 
never  attempted  to  classify  them. 

Mammals.  Mammals  are  considered  the  highest  ver- 
tebrates because  of  their 
complicated  structure 
and  because  of  their 
greater  mental  develop- 
ment. The  animals  in 
this  group  are  so  called 
because  they  produce 
milk,  a  secretion  of  the 
mammary  glands,  which 
is  used  as  food  for  the 
young.  The  young  of 

almost  all  mammals  are  born  fully  formed  and  then  for 
some  time  are  cared  for  by  the  parents.  The  skin  of 
mammals  is  partly  or  completely  covered  by  hairs. 


Fig:.  111.     Two  mammals. 


256 


A  YEAR  IN  SCIENCE 


There  are  about  3500  different  kinds  of  mammals. 
The  highest  of  these  is  man.  Very  similar  to  man  are 
the  monkeys,  apes,  gorillas,  and  chimpanzees.  Differing 
more  in  general  appearance,  but  still  having  the  charac- 
teristics of  mammals  are :  the  rat,  the  squirrel,  the 
beaver,  the  whale,  the  horse,  the  cow,  the  pig,  the  sheep, 
the  dog,  the  cat,  the  lion,  the  tiger,  and  the  bat.  Most 
of  these  forms  live  on  the  land,  but  a  few,  such  as 


Fig.  112.     Skeleton  of  squirrel. 

In  gnawing  mammals  the  canine  teeth  are  absent.  The  front, 
incisor,  teeth  grow  continuously  and  are  kept  sharp  by  the  gnawing 
on  hard  substances. 

whales,  porpoises,  and  sea-lions,  inhabit  the  ocean.  They 
are  all  air  breathing.  They  vary  greatly  in  size  from 
the  w^hale  and  the  elephant  to  very  small  mice  and 
moles.  Many  adaptations  to  habitat  and  methods  of 
life  occur  in  this  group.  Whales,  sea-lions,  and  por- 
poises have  the  limbs  modified  into  flippers  for  swim- 


GROUPS  OF  ANIMALS  257 

ming ;  mice,  beavers,  and  squirrels  have  the  front  teeth 
modified  for  gnawing ;  bats  have  the  fore  limbs  modified 
for  flying. 

Birds.     This  is  one  of  the  largest  groups  of  animals. 
It  has  boon  estimated  that  there  are  about  10,000  species 


Copyright  Detroit  Photographic  Co. 

Fig:.  113.  Sea  lions  are  modified  for  life  in  the  water.  Their 
feet  serV'C  as  swimming  organs  and  their  bodies  are  fish-like  in 
form. 

belonging  to  it.  Yet.  there  is  scarcely  another  group 
of  animals  so  easy  to  distinguish  at  sight  as  this.  The 
characteristics  common  to  all  birds  are :  the  body 
is  covered  with  feathers ;  the  fore  limbs  are  modified 
to  form  wings:  they  all  produce  eggs;  and  the  jaw  is 
always  covered  with  a  horny  substance  forming  a  bill. 
Birds  differ  greatly  in  their  habits  of  life  and  many 
interesting  adaptations  occur  in  this  group.  Some  birds 
have  the  feet  adapted  for  perching,  others  for  swim- 


258 


A  YEAR  IN  SCIENCE 


ming,  and  still  others  for  wading.  In  wading  birds, 
such  as  the  plover,  heron,  and  stork,  the  legs  are  very 
long.  In  perching  birds  there  are  three  toes  in  front 
and  one  behind.  This  hind  toe  is  important  in  holding 
the  foot  in  place.  The  tendons  and  the  muscles  in  the 
foot  and  leg  are  so  arranged  that  they  are  self  locking. 
Consequently  even  when  asleep,  such  birds  remain  bal- 
anced on  the  perch. 


Permission  of  Field  Museum   of  Natural  History, 
Fig.  114.     Adaptations  in  the  feet  of  birds. 

The  form  of  the  bill  varies  according  to  the  habits  of 
the  bird.  A  duck  has  a  flat  bill  for  pushing  through 
the  mud ;  the  woodpecker  has  a  sharp  bill  for  piercing 


GROUPS  OF  ANIMALS 


259 


the  barks  of  trees;  others,  such  as  the  vulture,  have 
strong,  curved  beaks  for  tearing  their  prey. 

In  many  ways  the  body  of  the  bird  is  especially  fitted 
for  flying.  Many  of  the  bones  of  the  skeleton  are  hol- 
low, thus  combining  lightness  and  strength.  The  breast 
bone  is  greatly  developed  for  the  attachment  of  the 


Permission   of  Field   Museum    of   Natural   History. 
Fig.  115.     Adaptations  in  the  bills  of  birds. 


large  muscles  used  in  flying.  The  rounded  body  with 
its  smooth  covering  of  feathers  offers  little  resistance 
in  flying. 

Because  of  the  very  active  life  of  birds,  the  rate  of 
respiration,  the  rate  of  the  heart  beat,  and  the  tem- 
perature of  the  body  are  all-  higher  than  in  any  other 
animal.  Birds  breathe  from  20  to  60  times  a  minute. 


260 


A  YEAR  IN  SCIENCE 


We  breathe  about  15  times  a  minute.  Our  temperature 
is  98.5°  F.,  while  that  of  birds  is  from  100°  F.  to  110°  F. 
The  migrating  and  nesting  habits  of  birds  afford 
much  interest  to  man.  The  song  and  beautiful  plumage 
give  us  much  pleasure ;  there  is  also  no  doubt  that  birds 

are  of  great  value  to 
man  in  the  destruc- 
tion of  insects  which 
destroy  plants. 

Reptiles.  To  this 
group  belong  snakes, 
lizards,  turtles,  and 
crocodiles.  Such  ani- 
mals are  character- 
ized by  the  covering 
of  scales  or  plates, 
they  breathe  by 
means  of  lungs,  they 
lay  eggs  very  similar 
to  those  of  birds,  and 
they  are  cold  blooded 
animals.  By  that 

we  mean  that  the  blood  is  not  always  warm  as  it  is  in 
mammals  or  birds. 

The  members  of  this  group  differ  greatly  among 
themselves.  The  turtle  is  peculiar  in  having  the  body 
covered  above  and  below  by  a  thick  shell  composed  of 
plates.  This  affords  an  excellent  place  for  retreat  in 
case  of  danger.  Like  the  turtle,  the  lizard  has  four 


Copyriglit  Henry  G.  Peabody. 
Fig.    116.     Humming  bird  feeding 
young-. 


GROUPS  OF  AXIMALS 


261 


legs  but  resembles  the  snake  in  the  scaly  covering  of 
the  body.     The  snake  is  perhaps  the  most  disliked  and 


Fig:.  117.     Snake. 

feared  of  all   the   animals.      This   is  scarcely   deserved 
because  most  snakes  are  harmless.     The  rattle-snakes, 
water  moccasins,  and 
copperheads   are   the 
commonest      of      the 
venomous  snakes. 

Amphibians.    (Am- 
phi,  both;  bios,  life). 
As    the    name    indi- 
cates, the  members  of      Photograph   by  American  Museum  of 
.,  .  Naturtu  History. 

this  group  pass  a  part  Fig.  118.    Green  turtle. 

of  their  lives  in  water 

and  the  other  part  on  land.  In  the  earlier  stages  of 
their  development  they  take  oxygen  out  of  the  water  by 
means  of  gills,  the  way  fish  do.  Later,  however,  they 


262 


A  YEAR  IN  SCIENCE 


lose  their  gills  and  breathe  by  means  of  lungs  as  do  the 
higher  animals.  The  body  is  covered  with  a  soft,  slimy 
skin.  Amphibians  are  also  cold  blooded  animals.  Frogs, 
toads,  and  salamanders  belong  to  this  group.  Some  of 


Fig.  119.     Stages  in  the^development  of  the  frog. 

these,  especially  the  salamanders,  greatly  resemble 
lizards.  From  these  animals  they  are  most  easily  dis- 
tinguished by  the  absence  of  scales. 


GROUPS  OF  ANTMAL8  263 

The  development  of  many  of  the  amphibians  is  inter- 
esting. The  eggs  of  the  frog,  for  example,  are  laid  in 
shallow  water  in  the  early  spring.  After  these  eggs 
are  fertilized  they  very  soon  hatch  into  "polywogs" 
or  tadpoles.  These  are  fitted  for  living  in  the  water. 
They  have  gills  for  breathing  and  a  tail  for  swimming. 
The  tadpole  grows  larger  and  gradually  the  outer  gills 
are  replaced  by  gills  which  grow  out  under  a  fold  of 
the  skin.  The  legs  soon  appear,  the  hind  ones  first. 
By  late  summer  lungs  have  developed;  the  legs  are 
Avell  grown;  and  the  tail  gradually  disappears,  being 
absorbed  into  the  other  parts  of  the  body.  About  this 
time  the  young  frog  leaves  the  water.  Its  food  is 
changed  from  a  vegetable  to  an  animal  diet,  chiefly 
insects.  In  some  kinds  of  frogs  it  takes  a  longer  time 
for  the  adult  frog  to  be  developed. 

When  marked  changes,  such  as  those  in  the  frog,  take 
place  in  the  development  of  animals,  the  process  is  called 
metamorphosis  (meta,  beyond;  morphe,  form). 

Fishes.  Fishes,  like  birds,  are  easily  recognized.  To 
this  group  belong  probably  as  many  as  13,000  different 
species.  It  is  the  largest  class  of  vertebrates.  Fishes 
resemble  each  other  in  the  following  characteristics: 
gills  are  used  in  breathing,  the  body  is  often  covered  with 
scales,  the  appendages  are  fin-like,  and  the  blood  is  cold. 

Fishes  are  well  fitted  for  their  life  in  water.  The 
shape  of  the  body  is  such  that  the  water  is  easily  ' '  cut, ' ' 
the  fins  and  large  tail  are  used  in  locomotion,  and  gills 
are  present  for  breathing.  The  air  sac  is  an  interesting 


264  A  YEAR  IN  SCIENCE 

organ.  When  this  is  filled  with  air,  the  body  of  the 
fish  has  nearly  the  same  weight  as  the  water  which  it 
displaces,  and  the  fish  is  thus  buoyed  up. 


Fig-.  "120.      White   perch. 

Arthropods.  This  group  of  animals,  together  with 
all  those  which  follow,  belong  to  the  invertebrates. 

The  arthropods  include  many  animals  which  you 
already  know.  It  is  an  exceedingly 'large  group,  and 
we  will  consider  it  in  three  divisions:  (1)  Crustacea, 
(2)  Insects,  (3)  Spiders.  All  arthropods  resemble  each 
other  in  a  few  characters:  their  bodies  are  made  up 
of  divisions  or  segments;  attached  to  some  of  these 
divisions  are  jointed  appendages;  all  have  a  hard  outer 
covering  on  the  body. 

To  the  Crustacea  belong  the  crayfish,  lobster,  crab, 
barnacle,  etc.  These  animals  have  a  hard  outer  shell. 
The  body  is  made  up  of  a  number  of  segments  to  which 
are  attached  many  appendages,  some  of  which  are  used 
for  claws,  others  for  walking  legs,  and  still  others  for 
swimming.  Crustacea,  for  the  most  part,  live  in  the 


GROUPS  OF  ANIMALS 


265 


water  and  breathe  by  means  of  gills.     Lobsters  and 
crabs  are  of  great  value  as  food  for  man.     Many  of 
the     smaller     crusta- 
ceans form  the  prin- 
cipal source  of  food 
for  fishes. 

The  insects  include 
more  species  than  all 
the  rest  of  the  ani- 
mal kingdom  put  to- 
gether. It  has  been 
estimated  that  •  there 
are  between  200,000 
and  1,000,000  differ- 
ent kinds  of  insects. 
To  this  group  belong 
butterflies,  moths, 
flies,  mosquitoes,  ants, 
bees,  wasps,  beetles, 
dragon  flies,  grass- 
hoppers,  crickets, 
cockroaches,  plant 
lice,  bugs,  etc.  Here 
also  belong  all  the 
caterpillars,  maggots,  and  grubs,  for  they  are  one  stage 
in  the  development  of  insects. 

Insects  have  the  body  divided  into  three  main  regions : 
head,  thorax,  and  abdomen.  To  the  thorax  are  attached 
three  pairs  of  legs,  and  usually  two  pairs  of  wings. 


Fig.   121.     Crayfish. 


Figr.  122.     Locust,  a  typical  insect. 


266 


A  YEAR  IN  SCIENCE 


Insects  breathe  by  means  of  air  tubes  which  are  con- 
nected with  the  outside  through  openings  in  the  sides  of 
the  body. 

Many  of  the  insects  undergo  complete  changes,  or 
metamorphoses,  when  they  develop.  For  example,  the 
egg  of  the  monarch  or  milkweed  butterfly  is  laid  in 
late  spring.  In  a  few  days  it  hatches  into  a  worm-like 
larva  called  a  caterpillar.  The  caterpillar  grows  very 


Fig-.  123.     Development  of  the  sphinx  moth;  L,  larva;  C,  chrysalis; 

A,  adult. 

rapidly  for  a  few  weeks.  Then  it  stops  eating  and 
begins  to  spin  a  mat  of  silk  upon  a  leaf  or  stem.  It 
attaches  itself  to  this  web  by  the  front  legs  and  hangs 
there.  After  about  twenty-four  hours  it  has  passed 
into  a  resting  stage  and  is  called  a  pupa,  or  chrysalis. 
After  a  week  or  more  of  inactivity,  the  shell  splits  and 


GROUPS  OF  ANIMALS 


267 


an  adult  butterfly  emerges.  In  moths  the  pupal  stage 
is  passed  in  a  cocoon  made  of  silk  or  other  material. 
Many  insects  pass  the  winter  in  this  quiescent  stage. 

Insects  are  of  great  interest  to  man  for  many  rea- 
sons. 1.  Many  adaptations  occur  in  insects.  2.  Bees 
and  ants  are  a  source  of  interest  because  they  live  in 
colonies.  3.  Many  insects  are  useful  to. man:  the  bee 
supplies  honey  and  wax;  the  silk  worm,  silk;  and  the 
lady  beetles  destroy  injurious  insects.  4.  Much  destruc- 
tion results  from  the  fact  that  many  insects  feed  upon 
plants  useful  to  man. 

The  spiders  differ  from  the  insects  in  the  absence  of 
wings  and  in  the  fact  that 
they  have  four  pairs  of  legs. 
The  nests  of  spiders  are  made 
of  a  silk-like  material  formed 
in  the  body  and  fashioned 
into  the  characteristic  web  by 
the  legs. 

Mollusks.  The  three  most 
common  members  of  this 
group  are  the  clam,  the  oyster, 
and  the  snail.  The  bodies  of 
these  animals  are  not  segmented  and  they  bear  no 
appendages.  They  are  soft  and  are  protected  by  a 
shell.  In  the  clam  and  the  oyster  this  shell  is  com- 
posed of  two  parts  called  valves.  It  is  formed  by  a 
fold  of  skin  known  as  the  mantle.  Over  the  inside 
of  the  shell  a  thin,  pearly  substance  is  formed 


Fig.  124.     A  spider. 


268  A  YEAR  IN  SCIENCE 

called  "mother-of-pearl."  Pearl  buttons  and  knife 
handles  are  made  from  the  shells  of  our  fresh  water 
clams.  Sometimes  an  irritation  is  produced  by  the 
presence  of  some  foreign  substance,  as  a  small  worm 
which  embeds  itself  in  the  mantle.  As  a  result  of  this 
irritation  masses  of  pearl  are  formed,  frequently  in 
concentric  layers,  around  the  irritating  substances. 
These  are  pearls  so  much  prized  as  ornaments.  Almost 
all  of  the  mollusks  live  in  the  water.  They  are  widely 
used  as  food  as  well  as  for  the  commercial  purposes 
already  referred  to. 

Worms.  You  are  familiar  with  this  group  from 
general  observation.  It  is  easy,  however,  to  mistake 
the  larvae  of  some  insects  for  members  of  this  group. 
The  bodies  of  worms,  such  as  the  common  earth  worm, 
are  composed  of  a  great  many  segments.  These  segments 
are  very  similar  in  structure.  Short  hair-like  feet,  not 
jointed,  are  present  011  many  of  them. 

Echinoderms.  These  ani- 
mals are  found  only  in  salt 
water.  Here  belong  the 
starfish  and  the  sea  urchin. 
The  echinoderms  are  all 
made  on  a  plan  of  five.  This 
is  very  evident  in  the  star- 
fish, which  has  the  five  arms 

A    starfish. 

radiating    from    a    central 

disc.  These  forms  usually  have  the  body  covered  with 
a  skeleton  bearing  spines. 


GROUPS  OF  ANIMALS 


269 


Coelenterates.  The  members  of  this  group  are  very 
simple  in  structure  being  tubular  in  shape  with  but  one 
opening  to  the  body.  Frequently  thread-like  ,  arms  aiv 
present  around  this  opening.  Sometimes  these  animals 
reproduce  by  a  process  called  budding.  A  small  knob- 
like  structure  grows  out  at  the  side  of  the  body  and 
gradually  becomes  larger  finally  forming  an  adult 
animal.  This  bud  may  break  off,  or  with  many  others 
like  it,  it  may  remain  attached  and  form  colonies.  Here 
belong  the  jelly-fishes, 
sea  -  anemones,  corals, 
and  hydras.  They  are 
all  found  in  water  and 
most  of  them  only  in 
salt  water. 

The  coral  has  long 
been  of  interest  because 
of  the  islands,  reefs, 
which  are  formed  by  the 
gradual  accumulation  of 
coral  shells,  and  also 

because  of  the  use  of  one 

kind  of  coral  for  ornaments. 

Porifera.  The  skeletons  of  some  of  the  representa- 
tives of  this  group  form  our  commercial  sponges. 
Sponges  live  in  colonies.  Each  of  the  largest  holes  in 
a  commercial  sponge  represents  the  central  body  cavity 
of  a  single  animal.  Sponges  are  very  simple  in  struc- 
ture; each  animal  consists  of  a  cup-like  structure  the 


126-     A  sea-anemone. 


270 


A  YEAR  IN  SCIENCE 


Permission  of  Field  Museum  of  Natural  History. 

Fig.  127.     A  group  of  marine  animals;  A,  starfish;  B,  sea  urchin; 
C,  coral ;  D,  sponge. 

walls  of  which  are  strengthened  and  supported  by  a 
hard  or  horny  substance.  All  except  a  very  few  of  the 
sponges  live  in  the  ocean.  Most  of  the  sponges  which 


Permission  of  Field  Museum  of  Natural  History. 
Fig.  128.     Drying  sponges,  Key  West,  Florida. 

are  used  for  commercial   purposes   come   from  off  the 
coast  of  Florida  or  from  the -Mediterranean  Sea. 

Protozoa.  These  are  the  simplest  animals,  and  like 
the  simplest  plants  they  consist  of  but  a  single  cell. 
They  are  found  in  any  water,  but  are  most  abundant 
in  stagnant  water.  Many  of  them  are  so  much  like  the 
one  celled  plants  that  it  is  impossible  to  draw  a  sharp 
line  between  them.  All  of  the  protozoa  are  very  small, 


GROUPS  OF  ANIMALS  271 

usually  invisible,  and  they  can  be  studied  only  with 
the  aid  of  a  microscope. 


Questions 

1.  Name  the  five  groups  of  vertebrates. 

2.  Give   examples   of   animals  belonging   to   Sach 
group  of  vertebrates. 

3.  State  the  principal  characteristics  of  each  of 
these  groups. 

4.  To  which  group  of  aninials  does  man  belong  ? 

5.  Describe   the   stages   through   which   the   frog 
passes  in  its  development. 

6.  Which  class  of  invertebrates  has  the  greatest 
number  of  species? 

7.  Which  groups  of  invertebrates  have   members 
which  are  of  economic  value  to  man  ? 

8.  Describe  the  development  of  a  butterfly. 

9.  From  what  animal  are  pearls  obtained? 

10.     To  which  group  do  the  simplest  animals  belong  ? 


CHAPTER  XXXIII 


ucleus 


Fig.     129. 


An    ameba. 
enlarged. 


Much 


LIFE  PROCESSES  IN  ANIMALS 

Ameba.  An  ameba  is  one  of  the  simplest  animals  in 
existence.  Since  it  is  composed  of  but  one  very  small 
cell,  its  life  can  not  be  made  up  of  many  complicated 

processes.  However,  it 
must  perform  certain 
functions  or  it  would 
not  be  alive.  By  study- 
ing the  few  functions 
which  an  ameba  does 
perform,  we  will  be 
able  to  determine  what 
processes  are  essential  to^the  life  of  any  animal. 

In  stagnant  water  there  is  often  found  an  irregular, 
jelly-like  mass.  If  this  is  carefully  observed  under 
a  microscope,  it  will  be  found  to  consist  of  one  cell 
containing  protoplasm  and  a  nucleus.  Imbedded  in  the 
protoplasm  are  particles  of  food.  Since  the  ameba  has 
no  mouth,  food  is  taken  into  the  body  by  a  very  simple 
method.  Projections  are  sent  out  from  the  body  which 
surround  the  food  and  envelop  it.  The  protoplasm  of 
the  cell  then  transforms  part  of  this  food  into  parts  of 
the  cell.  The  shape  of  the  ameba  gradually  changes  and 

272 


LIFE   PROCESSES  IN  ANIMALS 


273 


as  it  does  so  the  animal  moves,  frequently  leaving  waste 
products  in  its  path.  These  are  given  off  at  any  point 
on  the  body.  Amebas  also  breathe.  Oxygen  diffuses 


Fig.   130.     An  ameba  giving  off  waste  products. 

into  the  body  and  carbon  dioxide  is  given  off  in  the 

same  manner.    When  an  ameba  becomes  a  certain  size 

it  divides  into  two  nearly  equal  parts,  and  thus  two 

smaller  individuals  are  formed.     These  simple  animals 

are  also  sensitive  to   certain 

agencies,  stimuli,  acting  upon 

them.     They  are  sensitive  to 

some    extent    to    contact,    to 

heat,   to   chemical   conditions 

of  the  water,  to  food,  to  light, 

and  the  like. 

In  this   simple   animal   we 
find  the  following  processes: 

1.  It  takes  food  into  the  body. 

2.  It    digests   this   food.      3. 
It  gives  off  waste   products. 

4.  It  takes  oxygen  into  the  cell  and  carbon  dioxide  is 
given  off.  5.  It  moves.  6.  It  is  sensitive.  7.  It  repro- 
duces. From  the  simple  organization  of  this  animal 
we  may  infer  that  all  of  these  functions,  at  least,  are 
necessary  for  the  life  of  any  animal. 


Fig.  131.     Four  stages  in  the 
division   of  an  ameba. 


274 


A  YEAR  IN  SCIENCE 


Not  all  one  celled  animals  are  as  simple  in  structure 
as  the  ameba.  Neither  are  the  processes  in  these  ani- 
mals carried  on  in  such  a  simple  fashion.  In  many 
protozoa  the  body  is  fixed  in  form,  and  is  moved  by 
hair-like  projections,  cilia,  which  cover 
the  body.  There  is  often  a  permanent 
mouth  through  which  food  enters  the 
body,  and  definite  canals  through  which 
waste  products  leave  it. 

Complex  animals.  We  already  know 
that  by  far  the  greater  part  of  the 
animal  world  is  made  up  of  forms  much 
larger  and  more  complex  than  the 
ameba.  Most  animals  consist  of  collec- 
tions of  cells  living  together.  In  some 
animals,  such  as  the  sponge,  there  is 
very  little  difference  in  the  cells  which 
comprise  it.  In  other  forms,  like  the 
mammals,  there  are  innumerable  cells  of  which  there 
are  many  different  kinds. 

As  we  look  higher  in  the  animal  scale  we  find  that 
certain  parts  of  the  animal  are  set  apart  to  do  certain 
work  and  only  that  work.  In  a  community  of  people, 
there  are  some  men  who  do  manual  labor ;  others  who  are 
skilled  mechanics;  some  who  are  shopkeepers;  and  still 
others  who  are  professional  men.  Just  so,  wherever  an 
animal  is  composed  of  many  cells,  there  is  division  of 
labor.  Some  cells  are  fitted  to  do  one  kind  of  work, 
others  to  do  another  kind.  As  a  result  of  this  division 


Fig.  132.  Para- 
moecium,  a  one 
celled  animal, 
but  not  so  prim- 
itive in  struc- 
ture as  the 
ameba. 


LIFE  PROCESSES  IN  ANIMALS  275 

of  labor,  each  kind  of  work  in  the  body  of  an  animal 
is  performed  better  than  it  otherwise  would  be. 

Tissues,  organs,  and  systems.  As  soon  as  there  is  a 
difference  in  the  work  which  collections  of  cells  have 
to  do,  there  is  also  a  difference  in  the  structure  of  the 
cells.  A  collection  of  similar  cells  performing  the  same 
function  is  known  as  a  tissue  (see  page  196).  Several 
kinds  of  tissues  may  have  certain  functions  to  perform, 
together.  Such  a  group  of  tissues  forms  an  organ. 
Groups  of  organs  working  together  form  a  system. 
For  example,  a  certain  part  of  our  body  is  used  to  pre- 
pare the  food  so  that  it  can  be  used.  This  is  known  as 
the  digestive  system.  It  consists  of  a  number  of 
organs  such  as  the  stomach,  the  liver,  and  the  pancreas. 
Each  of  these  organs  in  turn  is  made  up  of  several 
tissues,  and  each  tissue  is  made  up  of  a  number  of  cells. 

In  the  higher  animals  certain  tissues  are  always 
present.  The  more  common  ones  are  muscle,  connective, 
epithelial,  bone,  and  nerve  tissues.  Each  of  these  is 
composed  of  cells  of  a  certain  structure  and  having 
certain  definite  properties. 

Animal  functions.  An  ameba,  we  know,  carries  on 
certain  processes.  These  same  general  processes  are 
carried  on  in  the  higher  animals.  The  difference 
between  an  ameba  and  a  dog,  for  example,  is  not  so 
much  in  what  each  does  as  in  the  way  that  it  is  done. 
In  other  words,  there  are  certain  general  processes 
which  must  be  performed  by  all  animals  if  they  continue 
to  live  successfully. 


276  A  YEAR  IN  SCIENCE 

These  fundamental  processes  are : 

1.  Digestion 

2.  Respiration 

3.  Circulation 

4.  Excretion 

5.  Motion 

6.  Sensitiveness 

7.  Reproduction 

Digestion.  Under  this  head  we  shall  include  all  the 
processes  connected  with  the  use  of  food.  It  must 
first  be  taken  into  the  body,  after  which  it  must  be 
changed  into  such  a  form  that  it  can  pass  into  the  body 
fluids. 

In  all  of  the  many  celled  animals,  food  when  taken 
into  the  body  passes  into  a  tube,  which  usually  extends 
throughout  the  length  of  the  body  and  has  two  open- 
ings. Occasionally,  there  is  only  one  opening,  the.  mouth. 

The  size  and  structure  of  this  tube  varies  in  different 
animals.  Usually  it  is  divided  into  several  regions, 
such  as  the  mouth,  the  throat,  the  esophagus,  the  stom- 
ach, and  the  intestines.  Frequently  this  latter  part 
is  very  much  elongated  so  that  the  length  of  the  digest- 
ive tract,  or  alimentary  canal,  is  very  much  greater 
than  the  length  of  the  body. 

Obviously,  so  long  as  the  food  is  in  this  tube  it  can 
not  become  a  part  of  the  body.  Both  the  solid  and 
liquid  foods  must  be  acted  upon  physically  and  chem- 
ically in  such  a  way  that  they  will  diffuse  through  the 
walls  of  the  alimentary  canal  and  into  the  vessels  carry- 


LIFE  PROCESSES  IN  ANIMALS  277 

ing  the  body  fluids.  This  preparation  for  diffusion  is 
known  as  digestion.  In  this  process  the  food  is  first 
broken  up  into  small  bits  and  parts  of  it  are  dissolved. 


Digestive 
Canal 


Fig.  133.  Diagram  of  a  longitudinal  section  of  a  hydra  showing 
a  simple  digestive  system  with  only  one  opening,  the  mouth.  Food 
is  digested  by  the  cells  lining  this  digestive  cavity. 

Then  some  chemical  action  takes  place.  This  is  brought 
about  by  juices  which  are  secreted  by  cells  lining,  or 
opening  into,  the  alimentary  canal.  Frequently  masses 
of  these  cells  form  organs,  called  glands,  whose  duty  it  is 


278  A  YEAR  IN  SCIENCE 

to  secrete  juices  for  digesting  the  food.  After  digestion 
the  food  diffuses  into  the  body  fluids.  This  process, 
known  as  absorption,  takes  place  principally  in  the 
intestines. 


Esophagus 


Mouth       Pharynx  Cr°P  Gizzard 


Fig.    134.      Section    of    an    earth   worm    Showing    the    parts    of    the 
alimentary  canal. 

Respiration.  The  different  cells  in  the  body  of  an 
animal  not  only  need  food,  but  also  oxygen.  This 
is  taken  into  the  body  from  the  medium  in  which 
the  animal  lives,  either  air  or  water.  By  means  of 
the  body  fluids  it  is  then  transferred  to  all  parts  of 
the  body.  The  oxygen  combines  with  some  of  the 
tissues  of  the  body,  and  as  a  result  of  this  process  of 
oxidation,  heat  and  energy  are  produced.  At  the  same 
time  certain  wraste  products  are  formed,  chief  of  which 
is  carbon  dioxide.  This  must  be  carried  to  some  organ 
that  can  eliminate  it  from  the  body.  This  whole  proc- 
ess, from  the  taking  in  of  oxygen  to  the  giving  off  of 
carbon  dioxide,  is  known  as  respiration. 

The  body  structure  necessary  for  this  process  may 
be  very  simple.  A  thin,  moist  membrane  filled  with  ves- 
sels containing  blood  or  some  other  fluid,  and  in  contact 
with  air  (or  water)  is  all  that  is  essential.  Such  a 
simple  respiratory  system  is  present  in  the  earthworm, 
in  which  the  skin  is  the  only  organ  used  in  breathing. 


LIFE  PROCESSES  IN  ANIMALS  279 

In  animals  living  in  the  water,  the  respiratory  organs 
consist  of  parts  outside  of  the  body  known  as  gills. 
In  other  animals  large  sacs  (lungs)  or  tubes  (in  insects) 
connect  with  the  outside  and  serve  as  stations  for  the 


Gills 

Fig.  135.     The  head  of  a  fish  with  the  operculum  removed  to  show 
the  breathing  organs,   the  gills. 

taking  in   of   oxygen   and   the   giving   off   of   carbon 
dioxide. 

Circulation.  In  a  very  small  animal,  such  as  an 
ameba,  the  food  and  the  oxygen  are  absorbed  any  place 
on  the  surface  of  the  body  and  pass  from  there 
into  all  parts  of  the  organism.  In  all  the  larger  ani- 
mals, however,  food  and  oxygen  are  taken  into  the 
body  in  special  regions  from  which  they  must  be  car- 
ried to  all  parts  of  the  body.  For  this  purpose  fluids 
are  necessary.  Generally  these  fluids,  blood  and  lymph, 
are  circulated  through  a  series  of  vessels.  Somewhere 
along  the  route  a  device  is  needed  for  forcing  the 
blood  through  these  vessels.  The  portion  set  aside  for 
this  work  constitutes  the  heart.  In  some  animals  this 
is  merely  a  thickened  portion  of  a  blood  vessel,  which 
as  it  contracts  forces  the  blood  along  in  the  tube.  To 
.prevent  the  fluid  from  flowing  in  both  directions  from 
the  heart,  valves  are  present.  In  the  higher  animals 


280  A  YEAR  IN  SCIENCE 

the  heart  becomes  a  complex  organ  divided  into  sepa- 
rate compartments  for  receiving  the  blood,  for  sending 
it  out,  and  for  keeping  the  blood  filled  with  oxygen 
separated  from  that  filled  with  carbon  dioxide. 

Excretion.  By  means  of  the  blood,  food  and  oxygen 
are  carried  to  the  body  tissues.  There  the  food  is 
used  for  building  up  the  broken  cells,  or  for  adding 
new  ones;  the  oxygen  unites  with  the  tissues  to 
produce  energy.  As  a  result  of  this  process  of  oxidation 
waste  products  are  formed,  chief  of  which  are  carbon 
dioxide,  water,  and  a  substance  called  urea,  containing 
compounds  of  nitrogen.  These  substances,  if  allowed 
to  accumulate,  seriously  interfere  with  the  action  of  the 
cells.  It  is  necessary,  therefore,  that  they  be  carried 
directly  to  organs  which  can  eliminate  them  from 
the  body.  This  removal  of  waste  products  from  the 
body  is  called  excretion.  In  all  animals  the  carbon 
dioxide  is  removed  by  the  respiratory  organs.  For  the 
elimination  of  the  other  waste  products  special  organs 
are  present.  In  the  lower  animals  these  are  often  sim- 
ple tubes  opening  to  the  outside  of  the  body,  but  in 
all  of  the  higher  animals  a  complex  organ,  the  kidney, 
is  used  for  this  purpose. 

Motion.  Motion  is  necessary  for  the  life  of  an  animal. 
In  the  ameba  we  found  that  this  ability  to  move  was 
in  the  protoplasm  itself.  In  the  higher  animals  this 
power  of  motion  is  characteristic  of  certain  cells  form- 
ing muscle  tissue.  This  tissue  is  present  wherever  there 
is  motion.  In  most  animals  special  appendages,  such 


LIFE  PROCESSES  IN  ANIMALS  281 

as  legs  or  wings,  are  present,  the  movement  of  which 
makes  locomotion  possible.  Sponges  and  corals,  on  the 
other  hand,  are  always  attached  and  can  not  move  from 
place  to  place. 

Sensitiveness.  Even  the  simplest  one  celled  animals 
respond  to  certain  stimuli.  If  a  point  on  one  side  of 
the  body  is  touched  in  some  way,  a  message  is  con- 
ducted to  all  parts  of  the  cell  and  the  animal  moves. 
As  animals  increase  in  complexity  they  become  more 
sensitive,  and  special  organs  are  developed  for  special 
senses.  An  earthworm,  for  example,  is  sensitive  to 
light  and  darkness.  It  has  no  eyes,  but  all  of  the  skin 
near  the  head  end  is  sensitive  to  light.  In  higher 
animals  well  developed  eyes  are  present,  which  can  not 
only  distinguish  between  light  and  darkness,  but  also 
between  colors.  Animals  also  have  special  organs  which 
are  sensitive  to  touch,  others  to  sound,  and  still  others  to 
odors.  From  these  special  structures  the  message  is 
not  transferred  from  cell  to  cell  and  thus  to  all  parts 
of  the  body,  but  it  travels  along  definite  tracts  (nerves) 
which  carry  it  to  a  central  organ,  in  higher  animals 
the  brain.  From  this  central  organ  messages  are  sent 
out  to  muscles  which  cause  them  to  act  and  produce 
motion. 

The  brain  and  nerves  not  only  make  it  possible  for 
animals  to  see.  hear,  and  feel,  but  they  also  keep  all 
parts  of  the  body  working  together  harmoniously. 

Reproduction.  The  length  of  time  which  animals  live 
varies  greatly.  Many  smaller  forms,  such  as  insects,  live 


282 


A  YEAR  IN  SCIENCE 


only  one  season,  while  elephants  are  known  to  live 
two  hundred  years.  Sooner  or  later,  however,  each 
animal  dies.  Frequently  death  is  due  to  some  external 
cause,  such  as  disease  or  injury.  If  not,  the  cells  of  the 
body  gradually  lose  the  power  to  perform  the  functions 
of  growth  and  repair,  and  finally  all  the  life  processes 
cease.  Since  animals  persist  on  earth,  evidently  new 
ones  are  constantly  being  formed.  This  process  of  pro- 
ducing new  individuals  is  known  as  reproduction. 

In  the  one  celled  animals  this  process  is  very  simple. 
After  an  ameba,  for  example,  reaches  a  certain  size, 


Fig.    136.      Four    stages    in 
division  of  an  ameba. 


the 


Fig.  137.  Hydra  show- 
ing1 a  bud.  Budding  is 
one  method  by  which  ani- 
mals may  reproduce. 


the  whole  cell  divides  into  two  nearly  equal  parts,  each 
of  which  is  a  perfect  but  smaller  individual.  Some- 
times, as  in  sponges,  hydras,  and  corals,  reproduction 
takes  place  by  budding.  A  small  knob-like  outgrowth 
appears  on  the  side  of  a  sponge.  This  gradually 


LIFE  PROCESSES  IN  ANIMALS  283 

increases  in  size,  and  finally  a  complete  new  sponge  is 
formed. 

In  all  higher  animals  certain  organs  of  the  body  are 
used  for  reproduction,  just  as  certain  organs  are  used 
for  digestion  or  for  respiration.  In  these  organs  two 
kinds  of  cells,  egg  and  sperm  cells,  are  produced.  The 
egg  cells  are  formed  in  the  ovary  which  is  a  structure 
present  in  the  female,  and  the  sperm  cells  are  formed 
in  the  spermary  of  the  male.  One  of  these  egg  cells 
unites  with  one  of  the  sperm  cells,  and  a  fertilized  egg 
is  formed.  The  single  large  cell  then  divides  a  great 
many  times,  and  gradually  a  new  animal  is  formed, 
which  is  like  the  parents  which  produced  it,  except 
smaller  and  younger. 

All  higher  animals  commence  life  as  a  single  cell 
formed  by  the  union  of  two  cells,  one  from  the  male  and 
one  from  the  female.  The  development  of  the  animal 
from  this  cell  varies  in  different  animals.  In  many 
animals,  such  as  the  frog,  the  fish,  the  reptile,  and  the 
bird,  there  is  often  attached  to  this  cell  a  large  amount  of 
food  material  forming  what  is  known  as  an  egg.  As 
the  young  animal  develops  in  this  egg  it  lives  upon  this 
food.  In  all  mammals  the  egg  develops  into  a  young 
animal  within  the  body  of  the  mother.  The  new  indi- 
viduals are  then  born  with  the  various  structures  of 
the  body  well  formed. 


984  A  YEAR  IN  SCIENCE 

Questions 

1.  Where  does  the  ameba  live? 

2.  What  is  the  structure  of  an  ameba? 

3.  Name  the  processes  which  are  carried  on  by 
the  ameba. 

4.  How   does   the   ameba  perform   each   of   these 
processes? 

5.  Compare    the    paramoecium    with    an    ameba. 
Which  is  the  more  complex  in  structure? 

6.  What  are  the  advantages  of  division  of  labor 
in  an  animal? 

7.  Define    and   give   examples   of  tissues,   organs, 
and  systems. 

8.  Why  is  it  necessary  for  animals  to  digest  the 
food  which  they  eat? 

9.  In  what  part  of  the  body  does  digestion  take 
place  ? 

10.  Why  is  it  impossible  for  animals  to  live  without 
oxygen? 

11.  What  is  the   source   of   carbon  dioxide  in  an 
animal  ? 

12.  Compare  the  respiratory  organs  of  the  earth- 
worm with  those  of  man. 

13.  From  what  source  do  fish  obtain  their  oxygen 
supply?      What    kind    of   breathing    organs    do    they 
have? 

14.  What  are  the  principal  functions  of  the  circula- 
tory system  ? 

15.  Name  three  waste  products  formed  in  animals. 

16.  Define  excretion. 

17.  What  is  the  name  of  the  tissue  in  animals  which 
is  used  to  produce  motion? 


LIFE  PROCESSES  IN  ANIMALS  285 

18.  Of  what  use  to  an  animal  is  the  nervous  system  ? 
What  are  the  principal  parts  of  this  system? 

19.  How  long  do  animals  live? 

20.  If  possible,   ascertain  the   average  number   of 
years  which  man  lives. 

21.  How  can  you  account  for  this  low  figure  ? 

22.  HOWT  do  one  celled  animals  reproduce? 

23.  What  is  an  egg  cell?    A  sperm  cell? 

24.  What  is  a  fertilized  egg? 

25.  What  is  the  function  of  the  white  arid  the  yolk 
of  a  chicken's  egg? 


CHAPTER  XXXIV 
RELATION  OF  ANIMALS  TO  MAN 

General  statement.  Man  is  dependent  upon  other 
forms  of  life  for  subsistence.  So  varied  and  numerous 
are  the  relations  of  animals  to  human  life  and  welfare 
that  members  of  all  the  various  groups  of  animals 
affect  human  interests  in  one  way  or  another.  To 


Photograph  by  Henry  G.  Peabody. 
Fig.  138.     Bison  in  Rocky  Mountain  Park,  Canada. 
This  fine  animal  has  been  hunted  for  its  skin  and  flesh  until  it 
is  now   practically   exterminated. 

realize  this,  we  need  only  to  refer  to  some  of  the 
facts  which  concern  us  most  directly  regarding  animals 
which  we  use  for  food,  such  as  cattle,  sheep,  swine,  fish, 
frogs,  turtles,  oysters;  those  which  furnish  clothing 

286 


RELATION  OF  ANIMALS  TO  MAX  287 

materials — wool,  furs,  and  silk;  those  which  attack  our 
crops;  those  which  attack  us  and  produce  diseases  or 
those  which  carry  them ;  those  which  invade  our  dwellings 
and  feed  upon  our  clothing  or  stored  foods;  or  still 
others  which  are  annoying  or  dangerous  because  of  their 
stings  or  bites. 

Many  of  our  greatest  industries  and  most  impor- 
tant articles  of  commerce  are  dependent  upon  animals 
which  furnish  food  supplies  or  clothing  material,  such 
as  beef,  milk,  butter,  wool,  furs,  eggs,  buttons,  ivory, 
bone,  oysters,  fish,  ostrich  plumes,  feathers,  honey,  wax, 
silk,  lac,  cochineal  dyes,  hair,  etc. 

Animals  useful  to  man.  Under  this  head  we  shall 
consider  (1)  domesticated  animals;  (2)  animals  used 
for  food;  (3)  animals  producing  materials  for  clothing. 

Domesticated  animals.  In  the  early  stages  of  civili- 
zation man  began  to  domesticate  animals.  At  first 
these  animals  were  probably  used  to  aid  in  the  hunt- 
ing and  capture  of  other  animals  for  food.  Gradually 
they  were  used  for  riding,  for  cultivating  the  soil,  and 
for  carrying  loads.  We  scarcely  appreciate  the  money 
value  at  the  present  time  of  horses,  cows,  poultry,  and 
other  domesticated  animals. 

Food-supplying*  animals.  Among  the  invertebrates 
we  find  some  very  important  food-supplying  animals, 
the  most  valuable  of  which  are  the  lobster,  crab,  oyster, 
and  clam.  To  some  extent  the  mussel  and  the  snail 
are  used  as  food.  The  lobster  is  highly  esteemed  in 
this  respect,  and  is  rapidly  disappearing  from  our 


288  A  YEAR  IN  SCIENCE 

coast  as  a  result  of  over  fishing.  The  animal  value  of 
the  lobsters  taken  on  the  North  Atlantic  coast  is  about 
$15,000,000.  The  oyster  industry  is  even  more  profit- 
able, aggregating  over  $50,000,000  a  year.  Every  class 
of  vertebrates  furnishes  species  used  as  food.  The 
total  annual  value  of  the  fisheries  of  the  United  States 
is  over  $50,000,000.  Frogs  and  turtles  are  edible,  but 
are  of  minor  importance  for  food.  Many  kinds  of  birds 
are  eaten,  furnishing  annually  hundreds  of  millions  of 
dollars '  worth  of  food  to  man.  To  the  mammals  belong 
the  cow,  the  swine,  and  the  sheep,  the  animals  which 
supply  most  of  our  meat.  Besides  meat,  chickens  fur- 
nish eggs,  and  cows  furnish  milk,  butter,  and  cheese. 
Animals  supplying'  clothing.  We  derive  most  of  the 
materials  from  which  our  clothing  is  made  from  plants. 
But  the  use  of  feathers,  furs,  skins,  and  wool  of  animals 
for  clothing  materials  is  of  considerable  importance. 
From  the  invertebrates  only  one  product  is  obtained, 
but  that  is  of  great  value.  When  the  caterpillar  of  the 
silk  worm  moth  goes  into  the  resting  stage,  it  forms 
a  cocoon  made  of  silk  secreted  by  glands  in  its  body. 
The  worms  are  killed  by  putting  the  cocoons  into  hot 
water,  and  then  the  silk  is  unwound.  From  these  silk 
threads  one  of  our  most  expensive  fabrics  is  made.  The 
silk  industry  is  of  much  importance  in  China  and  Japan. 
It  has  not  proved  profitable  in  the  United  States 
because  of  the  high  cost  of  labor.  Our  principal  source 
of  clothing  is  the  vertebrate  animals,  more  especially 
the  mammals.  From  these  we  obtain  a  great  variety 


RELATION  OF  ANIMALS  TO  MAN  289 

of  furs,  the  choicest  of  which  come  from  the  ermine, 
the  seal,  the  sable,  the  beaver,  the  mink,  the  fox,  the 
squirrel,  and  the  skunk.  Cheaper  furs  are  obtained 
from  the  cat,  the  dog,  the  raccoon,  and  the  rabbit.  From 
the  skin  of  the  coarser  haired  animals,  such  as  the  cow, 
the  sheep,  and  the  horse,  leathers  are  made. 

Animals  injurious  to  man.  Animals  are  injurious  to 
man  directly  or  indirectly  in  many  ways.  We  will 
consider  only  those  forms  (1)  which  produce  or  carry 
human  diseases,  and  (2)  which  are  injurious  to  crops. 

Diseases  produced  and  carried  by  animals.  Within 
recent  years  we  have  learned  that  yellow  fever,  malaria, 
smallpox,  sleeping  sickness,  and  some  other  diseases  are 
caused  by  the  presence  and  growth  of  one  celled  animals 
(protozoa)  in  the  human  body.  Long  ago  it  was  dis- 
covered that  various  parasitic  worms,  such  as  the  tape- 
worm and  the  trichina,  lived  in  our  bodies  and  were  the 
causes  of  pain  and  injury  to  the  body.  More  recently  the 
hook-worm  has  been  found  to  be  responsible  for  much  of 
the  laziness  and  shiftlessness  of  "the  poor  whites"  of  the 
South.  The  entire  South  undoubtedly  has  been 
retarded  in  its  development  by  this  parasite.  Not  only 
are  some  diseases  produced  by  animals,  but  some  dis- 
eases are  spread  by  them.  The  mosquito  and  fly  carry 
malarial  fever  and  typhoid  fever,  the  tse-tse  fly  carries 
sleeping  sickness,  and  the  flea  carries  bubonic  plague 
from  rats  to  man. 

Animals  injurious  to  crops.  Insects  do  the  greatest 
damage  to  crops.  Experts  estimate  that  insects  rob 


290 


A  YEAR  IN  SCIENCE 


Permission  of  U.  S.  Dept.  of  Agricul- 
ture. 

Fig.  139.  The  tussock  moth  is  a 
common  insect  injurious  to  shade  trees. 
F,  adult  female ;  E,  adult  male ;  D, 
larva;  K,  females  laying  eggs  on  bark 
of  tree ;  /,  pupae  in  cocoons. 


Permission  of  U.  S.  Dept.  of  Agriculture. 

Fig.  140.     The  potato  beetle  is  one  of  the 

best  known  of  the  garden  pests. 


us  each  year  of  about 
$500,000,000  worth  of 
crops,  forest  trees, 
and  lumber.  There 
are  thousands  of  dif- 
ferent kinds  of  these 
pests.  Some  devour 
foliage,  others  attack 
fruits  and  seeds,  and 
still  others  bore  into 
the  wood  of  the  tree 
on  which  they  live. 
In  combating  with 
insects  the  farmer 
is  assisted  and 
directed  by  the 
Bureau  of  Entom- 
ology of  the  United 
States  Department 
of  Agriculture  and 
by  various  state 
experimental  sta- 
tions. The  most 
effective  means  of 
control  thus  far 
found  is  by  poison- 
ous sprays.  By 
this  method  both 
the  adult  and  the 


RELATION  OF  ANIMALS  TO  MAN 


291 


Permission  of  U.  S. 
Dept.  of  Agricul- 
ture. 

Fig.  141.  Boll- 
weevil,  one  of  the 
most  important  en- 
emies of  cotton 
plants. 


Permission  of  U.  S. 
Dept.  of  Agricul- 
ture. 

Fig.  142.  Codling 
moth;  A,  adult;  B, 
larva  in  apple;  C, 
pupa  or  chrysalis. 


After  U.  S.  Dept.  of  Agriculture. 
Y\K    143      Corn  plant  two  feet  tall  infested  with  chinch  bugs.    Adult 

enlarged. 


292 


A  YEAR  IX  SCIENCE 


young  insects  are  killed.  A  newer  method  of  fighting- 
insects  is  the  introduction  of  one  species  of  insect  to 
attack  and  to  keep  in  check  another  species  of  insect. 
This  method  has  proved  quite  successful  in  the  Cali- 
fornia orange  orchards.  It  was  found  that  a  little  black 
and  red  beetle  of  Australia  fed  upon  one  of  the  scale 
insects  which  was  very  injurious  to  orange  trees.  These 


Fig:.   144. 


Permission  of   U.  8.  Dept.  of  Agriculture. 
Australian  ladybird  beetle  and  fluted  scale  ;   A,  larvae 


of  beetle  feeding  on  scale;  B,  pupa  of  beetle;  C,  adult  beetle ;  D 
orange  twig  showing  scales  and  beetles. 

beetles  were  introduced  into  scale-infested  orange 
orchards.  They  increased  in  numbers,  fed  upon  the 
scale  insects,  and  in  a  few  years  practically  relieved  the 
California  growers  of  all  anxiety  concerning  the  scale 
insects. 

Questions 

1.  Name  the  principal  domesticated  animals. 

2.  Learn,  if  possible,  from  what  wild  form  each 
of  these  has  come. 


RELATION  OF  ANIMALS  TO  MAN  293 

3.  Name  five  animals  used  by  man  as  food. 

4.  Is  the  federal  government  justified  in  maintain- 
ing a  Bureau   of  Fisheries?     Give   reasons  for  your 
answer. 

5.  From  what  animals  do  we  derive  materials  for 
clothing  ? 

6.  How  is  artificial  silk  manufactured? 

7.  Name    three    diseases    caused    by    one    celled 
animals. 

8.  Name  two  parasitic  worms. 

9.  From    government    pamphlets,    or    elsewhere, 
learn  what  you  can  of  the  history  of  the  hookworm. 

10.  What  is  one  of  the  functions  of  the  Bureau  of 
Entomology  ? 

11.  Is  it  important  for  us  to  know  how  to  combat 
insect  pests"? 

12.  What  are  some  of  the  common  insects  injurious 
to  crops  in  the  locality  where  you  live? 

13.  Name  the  pests  of  shade  and  fruit  trees  in  your 
region. 


CHAPTER  XXXV 

MAN'S  PLACE  IN  NATURE 

Classification.  In  our  study  of  the  classification  of 
animals  we  learned  that  man  is  a  member  of  the  mam- 
mals, the  highest  group  of  vertebrates.  The  particular 
class  of  mammals  which  includes  monkeys,  apes,  and 
man  is  known  as  the  primates.  In  body  structure  all 
the  members  of  this  class  are  very  similar,  the  gorilla 
being  most  like  man. 

The  greatest  difference  between  man  and  the  man- 
like apes  is  not  in  structure  but  in  intelligence.  There 
is  a  great  mental  gap  between  man  and  the  most 
intelligent  of  the  apes,  the  chimpanzee!  However,  there 
undoubtedly  once  lived  on  the  earth  races  of  men  who 
were  of  a  much  lower  scale  of  mental  development  than 
the  present  inhabitants. 

Differences  between  man  and  other  primates.  Struc- 
turally there  are  some  very  apparent  differences 
between  man  and  the  other  primates.  Man  is  more 
erect  in  position.  The  back  of  the  head,  the  cranium, 
is  relatively  larger  in  man,  thereby  balancing  the  head 
on  the  vertebral  column.  The  arms  are  much  shorter ; 
the  thumb  is  well  developed  and  can  be  opposed  to  the 
fingers ;  the  great  toe  is  smaller  and  can  not  be  opposed. 

294 


MAN'S  PLACE   IN  NATURE  295 

The  legs  in  man  are  better  developed  and  the  hip  bones 
are  large  enough  to  support  the  body  in  an  upright 
position.  The  brain  is  much  more  developed  and  much 


Fig.    145.      Chimpanzees. 

larger,  weighing  in  the  average  man  two  or  three  times 
that  of  the  gorilla.  Because  of  the  greater  develop- 
ment of  the  brain,  the  modes  of  life  and  the  other 
activities  resulting  from  a  high  grade  of  intelligence 
clearly  separate  man  from  the  lower  primates. 

Age  and  races  of  man.  The  first  men,  undoubtedly, 
lived  much  as  the  lower  animals  now  live.  They  wan- 
dered about  from  place  to  place  living  upon  whatever 
they  could  kill.  Gradually  they  began  to  use  imple- 
ments, the  first  of  which  were  made  of  stone.  These 
implements  were  at  first  used  as  weapons  to  aid  in  the 
capture  of  prey  for  food.  As  civilization  advanced, 
implements  were  made  of  bone,  and  then  later,  copper,, 
bronze,  and  iron.  Finally  man  began  to  domesticate 
animals,  to  cultivate  the  fields,  and  to  have  a  fixed 


296  A  YEAR  IN  SCIENCE 

place  of  abode.  Man  lived  in  this  way  for  thousands 
of  years.  Remnants  of  the  implements  which  he  used 
have  been  found,  but  we  have  no  other  records  of  the 
history  of  primitive  man.  The  earliest  monuments  and 
inscriptions  which  we  have  date  back  more  than  six 
thousand  years. 

There  exist  upon  the  earth  at  present  at  least  three 
varieties  of  man.  Each  of  these  differs  from  the  others 
in  external  appearance,  in  instincts,  and  in  social  cus- 
toms. These  three  varieties  are :  (1)  The  white  or 
Caucasian;  (2)  the  yellow  or  Mongolian;  (3)  the  black 
or  Ethiopian.  To  these  are  often  added  the  brown  or 
Malay  race  of  the  islands  of  the  Pacific,  and  the  red 
or  American  Indian. 

The  human  body.  In  our  present  study  we  are  espe- 
cially interested  in  man  as  he  exists  to-day.  It  is  impor- 
tant for  each  of  us  to  know  how  the  human  body  is 
constructed  (anatomy);  what  work,  or  function,  each 
part  of  the  body  must  perform  and  how  this  is  accom- 
plished (physiology);  and  finally,  how  to  care  for  the 
body  in  such  a  way  that  all  its  parts  are  working- 
normally,  and  consequently  are  in  good  health  (hygiene). 

We  can  not  properly  care  for  the  body  unless  we 
know  its  structure  and  its  functions.  We  often  under- 
estimate the  value  of  such  knowledge  concerning  the 
parts  of  the  body  used  in  digesting  the  food,  the  struc- 
tures used  for  admitting  air,  or  getting  rid  of  waste 
materials.  Such  knowledge  may  be  of  great  aid  to  us. 
Health  is  wealth.  It  not  only  leads  to  material  wealth, 


MAN'S   PLACE   IN  NATURE  997 

such  as  money,  but  it  is  necessary  for  the  greatest  hap- 
piness. We  all  know  how  expensive  sickness  is,  and 
we  also  know  how  much  human  misery  it  brings.  In 
order  to  better  understand  the  body,  which  is  so  like 
a  complicated  machine,  it  is  necessary  to  study  the 
structure  of  its  parts  and  their  different  functions. 
Only  in  this  way  is  it  possible  to  understand  the  human 
body  as  a  whole. 

Questions 

1.  Name  three  animals  belonging  to  the  primates. 

2.  Discuss  the  differences  between  man  and  the 
other  primates. 

3.  What  do  you  know  about  the  history  of  man  ? 

4.  What  sources  do  we  have  for  estimating  the 
age  of  man? 

5.  Name  the  chief  races  of  men.     Where  is  each 
found  ? 

6.  Why  is  it  of  value  to  you  to  know  something 
about  your  body? 


CHAPTER  XXXVI 
FOODS 

Introduction.  In  construction  work  the  building 
materials  which  we  use  depend  upon  the  kind  of 
building  which  we  expect  to  erect.  Sometimes  we  use 
bricks  and  cement,  other  times  we  use  wood  and  nails. 
From  time  to  time  the  building,  after  its  completion, 
needs  repair.  Parts  decay  or  become  worn  and  have 
to  be  replaced  by  new  material ;  or,  sometimes,  additions 
are  made  to  the  original  building. 

Much  the  same  principle  holds  true  for  the  living 
world,  plants  and  animals.  Each  plant  and  each  animal 
is  constantly  being  worn  out  and  being  added  to.  The 
building  materials  which  are  supplied  to  the  plant  or 
to  the  animal  we  call  food. 

Elements  in  food.  This  food,  obviously,  must  con- 
tain the  elements  of  which  the  plant  or  animal  is  com- 
posed. Since  all  living  material  is  much  the  same  in 
chemical  composition,  both  plants  and  animals  need 
about  the  same  elements.  In  the  human  body  those 
elements  which  are  most  common  are  carbon,  hydro- 
gen, oxygen,  nitrogen,  calcium,  phosphorus,  sulphur, 
sodium,  chlorine,  fluorine,  potassium,  and  iron. 

Use  of  food.     We  need  food  for  exactly  the  same 

298 


FOODS  299 

reasons  that  the  plant  does :  first,  for  growth ;  second, 
for  the  repair  of  tissues  worn  out  in  doing  work; 
and  third,  for  producing  heat.  For  growth  we  need  foods 
which  contain  the  elements  which  are  found  in 
protoplasm.  Heat  is  produced  in  the  body  by  slow 
oxidation.  Foods  used  for  this  purpose  must  contain 
large  quantities  of  carbon,  since  most  of  the  energy 
in  the  body  is  produced  by  the  oxidation  of  carbon. 

Foodstuffs.  We  already  know  that  "we  can  not  live 
on  water,  carbon  dioxide,  and  mineral  matter  from  the 
soil.  These  simple  substances  constitute  the  raw  food- 
materials  for  plants,  but  they  can  not  serve  as  food  for 
us.  For  our  food  we  use  complex  chemical  compounds 
in  the  form  of  meats  and  vegetables.  Chemists  have 
analyzed  our  foods,  and  have  found  that  all  of  them  are 
composed  of  one  or  more  of  five  classes  of  compounds. 
These  are  known  as  the  foodstuffs.  The  most  important 
foodstuffs  are  proteins,  carbohydrates,  fats  and  oils, 
minerals,  and  water. 

Proteins.  Different  varieties  and  forms  of  protein 
are  found  in  nearly  all  kinds  of  animal  and  vegetable 
foods.  The  most  common  protein  foods  which  we 
obtain  from  animals  are  meat  (except  fat),  milk,  eggs, 
cheese,  and  gelatin.  Of  the  plants,  peas,  beans,  and  all 
cereals  except  rice  give  us  protein. 

The  proteins  are  often  called  the  nitrogenous  foods 
because  they  always  contain  large  quantities  of  nitro- 
gen. In  addition  to  nitrogen  they  contain  carbon, 
hydrogen,  oxygen,  sulphur,  and  sometimes  phosphorus 


300 


A  YEAR  IN  SCIENCE 


and  iron.    These  elements  form  complex  compounds,  the 
exact  composition  of  which  is  not  known. 


Water    73,7 


Fat  4.0 


Protein 
2.2 


FatOl 
Carbo- 
hydrate 18.4  POTATO 


Water  2.5 
Protein  16.6 


Fat   63.4 


Ash    1.4 


WALNUT 

Permission  U.  S.  Dejjt.  of  Agriculture. 
Fig.    146.      Showing    the    foodstuffs    in    different    foods. 

Test  of  protein.  There  are  a  number  of  ways  in 
which  the  presence  of  protein  in  food  may  be  detected. 
One  of  the  best  methods  is  the  use  of  nitric  acid  and 
ammonia.  Some  of  the  food  to  be  tested  is  placed  in  a 


FOODS  301 

test  tube,  and  strong  nitric  acid  is  added.  The  mixture 
is  heated,  and  if  protein  is  present  the  food  changes  to. 
a  yellow  color.  If  then  the  acid  is  poured  off,  and 
strong  ammonia  added,  the  yellow  color  changes 
to  a  deep  orange,  and  we  may  be  sure  protein  is 
present. 

Carbohydrates.  In  this  class  are  included  starches 
and  sugars.  The  carbohydrates  are  composed  of  three 
elements :  carbon,  hydrogen,  and  oxygen.  These  are  so 
combined  that  there  is  always  twice  as  much 
hydrogen  as  oxygen.  For  example,  the  formula 
for  common  sugar  is  C12H220llf  for  grape  sugar 
C6H1206,  and  for  starch  C6H1005. 

Starch.  Starch  is  formed  in  all  green  plants.  Fre- 
quently it  is  stored  in  the  cells  of  grain,  in  seeds,  and 
especially  in  stems  and  roots.  We  obtain  much  of  our 
starch  from  potatoes  and  bread. 

Test  for  starch.  Starch  when  treated  with  a  solu- 
tion of  iodine  turns  dark  blue.  This  is  the  test  usually 
employed  to  detect  the  presence  of  starch. 

Sugar.  Sugar  is  likewise  derived  from  plants.  There 
are  many  different  kinds  of  sugar;  for  example,  cane 
sugar,  grape  sugar,  and  milk  sugar.  These  substances 
differ  more  or  less  in  chemical  composition.  However, 
both  cane  and  milk  sugar  may  be  changed  into  grape 
sugar  by  boiling  them  with  hydrochloric  acid. 

Test  for  sugar.  In  the  test  most  commonly  used  to 
detect  the  presence  of  sugar,  a  mixture  called  Fehling's 
solution  is  used.  If  a  few  drops  of  this  solution  are 


302  A  YEAR  IK  SCIENCE 

added  to  a  solution  containing  grape  sugar  and  then 
boiled,  the  color  becomes  brick  red. 

Pats  and  oils.  Under  this  class  are  included  not  only 
what  we  ordinarily  understand  as  fat,  but  also  all 
vegetable  and  animal  oils.  Like  the  carbohydrates,  the 
fats  and  oils  contain  only  the  three  elements,  carbon, 
hydrogen,  and  oxygen,  but  in  different  proportions. 
They  have  a  much  lower  percentage  of  oxygen.  They 
are  all  lighter  than  water  and  insoluble  in  it. 

Test  for  fats  and  oils.  The  presence  of  fats  may  be 
detected  in  one  of  two  ways : 

(a)  Put   a  small  quantity   of  the   substance   to   be 
tested  on  a  piece  of  paper  and  slowly  heat  it.    If  fat  is 
present,  it  will  make  a  translucent  grease  spot  on  the 
paper. 

(b)  Fats  are  soluble  in  benzine  and  ether.    The  sub- 
stance to  be  tested  is  soaked  in  benzine  or  ether.    Then 
it  is  filtered.     If  the  solution  is  allowed  to  stand,  the 
ether  will  evaporate.    Fat,  if  present,  will  then  remain, 
because  it  does  not  evaporate. 

Mineral  salts  or  inorganic  foods.  Dissolved  in  ordi- 
nary drinking  water,  in  lean  meat,  and  in  vegetables 
are  many  forms  of  salts.  Only  one,  common  salt,  do 
we  add  to  our  diet,  All  salts  are  unburnable.  When 
foods  are  burned,  if  ashes  are  left  behind,  we  may 
conclude  that  mineral  matters  are  present. 

Water.  Nearly  59%  of  the  weight  of  our  bodies  is 
water.  Some  water  is  taken  into  the  body  directly, 
but  much  of  it  indirectly.  A  large  proportion  of  most 


FOODS  303 

of  our  foods  is  water.  As  we  know,  water  evaporates. 
This  enables  us  to  determine  the  quantity  of  water 
present  in  a  food  by  heating  it  until  dry.  The  loss  in 
weight  represents  the  amount  of  water  present. 

Questions 

1.  Name  the  principal  elements  found  in  the  body, 

2.  What  is  a  food? 

3.  State  two  reasons  why  we  need  food. 

4.  What  are  the  five  foodstuffs? 

5.  Name  the  elements  found  in  each  foodstuff. 

6.  What  is  the  test  for  each  foodstuff? 

7.  How  do  fats  differ  from  carbohydrates? 


CHAPTER  XXXVII 


COMPOSITION  OP  FOODS 

Content  of  foods.  The  extent  to  which  the  food 
stuffs  occur  in  some  of  our  foods  is  indicated  in 
the  following  table,  which  is  taken  on  the  authority  of 
the  United  States  Department  of  Agriculture.  The 


FOOD 

Pro- 
tein 

Carbo- 
hydrate 

Fat 

Water 

Ash 

Calories 
p'er 
Pound 

Beef  steak    .  . 

18.6 

0- 

18.5 

61  9 

1  0 

1090 

Veal,  leg  cut  

20 

0 

7 

68 

1.0 

695 

Mutton,  loin  
Pork  chop    

13 
16.9 

0 
0 

28 
30.1 

42 
52 

0.7 
1.0 

1415 
1535 

Fowl    

14 

0 

12 

47 

0.7 

765 

Fish,   mackerel    .  . 
Oysters   

18.3 
6.2 

0 
3.7 

7.1 
1.2 

73.4 
86.9 

1.2 
2 

620 
230 

Effffs  .  . 

14.8 

0 

10.5 

72.7 

1.0 

695 

Butter  

1.0 

0 

83.0 

13.0 

3.0 

3405 

Milk,  whole   
Cheese,  cream  .... 
Bread,  white   .... 
Bread,  whole  wheat 
Oat  breakfast  food 
Corn  meal    
Rice    . 

3.3 
25.9 
9.2 

9.7 
2.8 
9 
8 

5.0 
2.4 
53.1 
49.7 
11.5 
75 
79 

4.0 
33.7 
1.3 
0.9 
0.5 
2 
0.3 

87.0 
34.2 
35.3 
38.4 
84.5 
12 
12 

0.7 
3.8 
1.1 
1.3 
0.7 
1.0 
0.4 

315 
1885 
1180 
1110 
280 
1635 
1620 

Potato 

2.2 

18.4 

0.1 

78.3 

1.0 

375 

Beans,  green  string 
Beans,  shelled    .  .  . 
Corn,  green    
Apple 

2.3 
9.4 
3.1 
0.4 

7.4 
9.1 
9.7 
14.2 

0.3 
0.6 
1.1 
0.5 

89.2 
58.9 
75.4 
84.6 

0.8 
2.0 
0.7 
0.3 

190 
720 
460 

285 

Banana  

1.3 

22.0 

0.6 

75.3 

0.8 

445 

Strawberry 

1.0 

7.4 

0.0 

90.4 

0.6 

175 

Walnut  
Peanut    

16.6 

25.8 

16.1 
24.4 

63.4 
38.6 

2.5 
9.2 

1.4 

2.0 

3180 
2485 

304 


COMPOSITION  OF  FOODS  305 

carbohydrate  column  is  mostly  starch,  except  in  milk, 
where  it  is  all  sugar. 

The  amount  of  energy  yielded  when  a  pound  of  food 
is  oxidized  is  expressed  in  calories.  For  example, 
one  pound  of  butter  will  yield  3405  calories  of  heat 
and  one  pound  of  strawberries  only  175  calories.  The  ash 
content  represents  the  mineral  salts  present. 

According  to  this  table,  which  foods  will  yield  the 
most  protein  ?  Carbohydrate  ?  Fat  ?  Energy  ? 

Use  of  foodstuffs.  As  we  have  stated  before,  food  is 
used  for  the  repair  and  growth  of  the  body  and  to 
supply  energy  in  the  form  of  heat  or  action.  Energy 
is  the  ability  to  do  work.  Both  action  and  heat  are 
thus  forms  of  energy.  Foods  must  supply  the  body 
with  building  material  and  with  fuel. 

Building  material.  Some  foods,  the  nitrogenous 
ones,  supply  all  that  is  essential  for  the  growth  and 
repair  of  the  body.  We  would  expect  this  when  we 
recall  that  the  body  is  composed  of  cells,  that  cells 
contain  protoplasm,  and  that  protoplasm  and  protein 
are  nearly  identical  in  composition.  Mineral  salts  are 
known,  too,  to  share  in  this  repair.  Proteins  may  be 
oxidized,  but  this  is  not  their  principal  use. 

Fuel.  It  may  be  that  carbohydrates  and  fats  are 
used  as  building  materials,  but  their  principal  use  is  to 
serve  as  fuel.  When  they  are  oxidized  they  supply  heat 
and  power.  Fat  is  especially  suited  to  this  purpose; 
that  is  the  reason  why  inhabitants  of  cold  coun- 
tries eat  such  large  quantities  of  fatty  foods.  Some 


306  A  YEAR  IN  SCIENCE 

of  the  fat  and  also  some  of  the  carbohydrates  which 
we  eat  are  stored  away  in  the  body  to  be  kept  for 
future  use. 

Quantity  and  kind  of  food.  It  perhaps  has  never 
occurred  to  you  that  there  is  a  reason,  other  than  taste, 
why  we  have  certain  combinations  of  foods.  For 
example,  why  do  we  use  meat,  potatoes,  other  vegeta- 
bles, and  a  dessert  as  the  essential  parts  of  a  dinner? 
It  is  because  meat  supplies  protein  and  fats ;  vegetables, 
protein  but  principally  carbohydrates ;  and  dessert,  car- 
bohydrates. All  contain  mineral  salts  and  water. 
Together  they  give  us  a  better  balanced  ratio  of  the 
different  foodstuffs  than  any  one  food  alone  would 
give.  Variety  in  our  foods  also  appeals  to  the  taste. 
Enjoyment  of  our  foods  usually  adds  to  the  ease  with 
which  they  are  digested. 

It  is  difficult  to  determine  how  much  food  we  need. 
The  amount  varies  so  much  with  each  individual  that 
we  can  not  make  even  a  general  statement  of  much 
value. 

Selection  of  food.  Daily  in  each  home  a  selection  of 
food  must  be  made.  What  shall  determine  this  selec- 
tion? Shall  we  buy  the  foods  which  we  like  the  best? 
Shall  we  buy  the  foods  which  cost  the  least,  or  the 
ones  which,  according  to  market  prices,  are  highest 
priced?  It  must  be  apparent  to  you  that  not  any  one 
of  these  factors  is  al'one  sufficient  to  determine  this 
selection.  It  is  not  so  easily  solved  that  we  can  merely 
consult  our  tastes,  or  our  purses,  or  the  prices  which 


COMPOSITION  OF  FOODS  307 

conditions  render  necessary,  or  the  producer  pleases,  to 
place  on  his  goods. 

It  is  true,  these  factors  must  be  considered.  But 
first  we  must  determine  the  kind  of  food  which  will 
supply  the  materials  which  our  bodies  need.  The 
amount  of  protein  needed  will  vary  with  the  amount 
of  manual  labor  we  do,  the  amount  of  fat  and  carbo- 
hydrate with  the  energy  used,  and  also  with  the  tem- 
perature. The  highest  priced  foods  are  not  always  the 
most  nutritious.  Neither  is  it  always  economy  to  buy 
the  cheapest  foods.  The  problem  is  how  to  buy  the 
largest  amount  of  nutritious  food  for  the  least  money. 

Adulteration.  The  purchaser  must  also  consider  the 
relative  purity  of  foods.  This  is  especially  necessary 
in  different  brands  of  canned  goods.  Many  of  them 
contain  adulterants  or  preservatives  which  are  danger- 
ous to  the  health.  Legislative  measures  are  now  being 
taken  to  protect  the  public  against  adulterated  foods. 
A  national  law,  commonly  known  as  "The  Pure  Food 
Law,"  was  passed  in  1906  for  the  prevention  of  adulter- 
ation and  misbranding  of  foods  or  drugs.  This 
stimulated  further  state  legislation.  Now  nearly  every 
state  has  a  general  food  law  and  is  making  an  attempt 
to  enforce  it. 

Cooking1.  Some  foods,  like,  fruits,  milk,  and  nuts, 
are  eaten  without  being  cooked.  The  great  majority, 
however,  are  cooked.  As  a  result  of  cooking,  meats 
and  vegetables  are  more  easily  digested  and  are  made 
more  palatable. 


308  A  YEAR  IN  SCIENCE 

Sometimes  in  foods,  bacteria  and  other  parasites  are 
living.  Most  of  these  are  fortunately  destroyed  at  the 
temperature  of  boiling  water.  Trichina  and  tapeworm 
are  two  parasitic  worms  sometimes  present  in  meats 
in  a  so-called  resting  stage.  Trichina  is  found  in  pork. 
When  diseased  pork,  poorly  cooked,  is  eaten,  these 
small  worms  again  become  active.  They  bore  their  way 
through  the  walls  of  the  alimentary  canal  and  finally 
settle  in  the  muscles.  This  produces  a  painful  and 
sometimes  fatal  disease.  The  tapeworm  is  found  in 
pork  and  beef.  It  attaches  itself  by  means  of  hooks 
to  the  walls  of  the  alimentary  canal,  remains  there 
and  grows.  It  can  readily  be  removed  and  no  serious 
results  follow. 

Decay  in  meat  is  brought  about  by  bacteria.  If  the 
process  has  continued  far  enough  poisons,  called 
ptomaines,  are  produced.  The  bacteria,  but  not  the 
poisons,  can  be  rendered  harmless  by  heat.  As  a  result 
ptomaine  poisoning  frequently  follows  the  eating  of 
tainted  meats,  especially  fish,  and  spoiled  ice  cream. 

Milk  can  be  rendered  harmless  by  heating  it  for  half 
an  hour  in  water  at  a  temperature  of  140°F.  to  160 °F. 
It  should  then  be  cooled  and  kept  cool.  .This  process, 
known  as  pasteurization,  kills  the  bacteria  and  at  the 
same  time  obviates  some  of  the  disadvantages  of  boiling 
milk. 


COMPOSITION  OF  FOODS  309 

Questions 

1.  Name  five  foods  rich  in  protein.    In  starch.    In 
fats. 

2.  Which  foodstuffs  are  used  principally  for  build- 
ing materials?    For  fuel? 

3.  Explain  the  advantages  in  the  following  com- 
binations of  foods :     bread  and  butter,  ham  and  eggs, 
macaroni   and   cheese,   potatoes   and  meat,   pork   and 
beans. 

4.  Suggest  a  menu  for  a  breakfast.     For  a  lunch. 
For  a  dinner.    Explain  in  each  instance  why  you  made 
this  selection  and  combination  of  foods. 

5.  Upon  what  basis  should  one  make  his  selection 
of  food? 

6.  Would  it  be  wise  for  a  laboring  man  to  live  on 
potatoes  only,  just  because  they  were  cheap? 

7.  Why   should   the   food   which   we    eat   in   the 
summer  differ  from  that  which  we  eat  in  the  winter? 

8.  From   your   grocer   learn   the    price    of   foods. 
Using   this   information    and   the    table   on   page    304, 
suggest  foods  which  it  would  be  advisable  for  a  poor 
man  to  purchase. 

9.  What  is  meant  by  adulteration  of  foods? 

10.  What  are  pure  food  laws  ? 

11.  Why    should    we    always    read    the    labels    on 
canned  goods  and  drugs  before  purchasing  them? 

12.  Why  do  we  cook  our  foods? 

13.  What  are  ptomaines? 

14.  What  is  pasteurized  milk?    Certified  milk? 


CHAPTER  XXXVIII 

DIGESTIVE  SYSTEM 

Introduction.  We  have  just  discussed  the  composi- 
tion of  foods  and  the  uses  of  foods  to  the  body.  It  is 
evident  to  everyone,  however,  that  many  changes  must 
take  place  before  the  food  which  we  eat  can  become 
a  part  of  the  body.  These  changes  take  place  in  a  set 
of  organs  which  we  call  the  digestive  system.  This 
system  consists  of  two  parts,  the  alimentary  canal  and 
the  digestive  glands. 

Alimentary  canal.  The  alimentary  canal  is  a  long 
tube  extending  through  the  body  and  having  two 
openings,  the  mouth  at  one  end  and  the  anus  at  the 
other.  In  some  animals  this  tube  is  almost  straight 
and  of  about  the  same  diameter  throughout  the  body. 
In  man,  however,  it  is  over  thirty  feet  long  and  with 
a  diameter  which  varies  greatly. 

It  begins  at  the  mouth  opening,  enlarges  and  forms 
the  mouth  cavity,  which  in  turn  communicates  with  the 
smaller  throat  cavity.  Posterior  to  the  throat  is  a  tube 
which  is  called  the  gullet,  or  esophagus,  opening  into  an 
enlarged  pouch,  the  stomach.  From  the  stomach  the 
food  is  conducted  into  the  long  coiled  intestine,  which 
fills  most  of  the  lower  part  of  the  trunk  of  the  body. 

310 


DIGESTIVE  SYSTEM 


311 


Pleura 


Pericardium 


Intestine 


Peritoneum 


Bladd 


Fig.  147.  Diagram  showing  the  position  of  the  organs  in  the 
body  cavity  which  is  divided  by  the  diaphragm  into  thorax  and 
abdomen. 

Digestive  glands.  Connected  with  the  alimentary 
canal  are  a  number  of  glands.  The  digestive  juices 
which  act  chemically  upon  the  food  are  produced  by 
these  glands.  The  salivary  glands  pour  their  secretion 
into  the  mouth.  The  gastric  glands  open  into  the 
stomach.  The  secretions  from  .three  other  glands,  the 
intestinal,  the  liver,  and  the  pancreas,  flow  into  the 
intestine. 


312 


A  YEAR  IN  SCIENCE 


Mouth 


Pharynx 


Stomach 


The  mouth.  The 

cavity  of  the  mouth 
is  bounded  in  front 
and    at    the    sides 
by    the    lips,    the 
cheeks,      and     the 
teeth,    and    below 
by      the      tongue. 
The    roof    of    the 
mouth    is    formed 
by     a     horizontal 
plate  of  bone  called 
the     hard    palate. 
Near  the  middle  of 
the  mouth  the  hard 
palate     ends     and 
is  continued  back- 
ward  by   the   soft 
palate.       Hanging 
down      from      the 
roof  of  the  mouth, 
and   separating    it 
from  the  throat,  is 
the  uvula.     The  entire  cavity  is  lined  with  a  soft' moist 
covering  called  the  mucous  membrane.     This  membrane 
is  continuous  and  forms  the  inner  lining  of  the  whole 
alimentary  canal.     It  secretes  a  watery  fluid  known  as 
mucus. 

Teeth.     Within  the  mouth  are  the  teeth  which  are 


Small 
Intestine 


Appendix 


Large 
Intestine 


Figr.   148.     The  alimentary  canal. 


DIGESTIVE  SYSTEM 


313 


Sublingual 


Bile  Sac 


Parotid. 


-Submaxillary 


,  Liver 


set  in  sockets  formed  in  the  bone  of  the  upper  and 
lower  jaws.  In  a  complete  set  of  an  adult  there  are 
thirty  two  teeth. 
They  are  not  all 
alike.  In  front 
in  each  jaw  there 
are  four  teeth 
with  chisel  shaped 
edges,  the  incisors, 
which  are  used  for 
cutting  the  food. 
On  each  side  of 
these  there  is  one 
pointed  tooth.  Be- 
cause of  their  re- 
semblance to  the 
teeth  of  a  dog, 
these  two  teeth  are 
called  the  canine 
teeth.  Their  shape 
fits  them  for  tear- 
ing the  food.  Just 
behind  each  canine 
tooth  there  are  two 
teeth  which  have  the  biting  surface  divided  into  two 
parts.  These  are  the  bicuspids,  (Latin,  bis  meaning 
twice,  and  cuspis,  a  point).  The  three  teeth  on  each 
side  back  of  the  bicuspids  are  the  molars.  These  have 
broad  flat  surfaces  for  grinding  the  food  into  small 


Fig.   149.     The  digestive  glands. 


314 


A  YEAR  IK"  SCIENCE 


pieces.  The  last  molar  on  each  side  often  appears  as 
late  as  the  twentieth  year,  sometimes  later,  and  is  called 
a  wisdom  tooth. 


Eustachian  Tube 


Esophagus 


-Trachea 


Fig.  150.      Median   section   through   the  head   showing  the   relation 
of  the  mouth  and  nasal  cavities  to  the  esophagus. 

Structure  of  tooth.  The  portion  of  the  tooth 
embedded  in  the  bone  is  the  root  of  the  tooth ;  the 
exposed  portion  is  the  crown.  Covering  the  crown  is 
a  layer  of  enamel,  which  is  the  hardest  tissue  in  the 
body.  The  root  has  no  enamel,  but  is  covered  with  a 
layer  of  cement.  The  largest  part  of  the  tooth  is 
composed  of  a  bone-like  substance  called  dentine.  This 
surrounds  a  small  cavity,  the  pulp  cavity.  Through  a 


DIGESTIVE  SYSTEM 


315 


Enamel 


Fir.  151.     Lower  jaw  bone  with  the  teeth  in  place ;  1,  2,  S,  molars  ; 
4,  5,  bicuspids  ;  6,  canine ;   7,  8,  incisors. 

small    aperture    at   the    end   of    the    root,    nerves    and 
blood  vessels  enter  this  cavity. 

Care  of  the  teeth.  Enamel  is  not  a  living  substance 
and  can  not  be  repaired  when  injured.  Frequently  the 
enamel  is  cracked  or  worn  through.  This  may  be 
caused  by  picking  the  teeth  with  a  hard  instrument 
such  as  a  pin.  A  sudden 
change  in  temperature  is 
likely  to  crack  enamel.  Par- 
ticles of  food  sometimes 
remain  between  the  teeth. 
These  decay  and  form  an 
acid  which  destroys  the 
enamel.  After  this,  decay  Bone 
takes  place  rapidly  in  the 
soft  dentine. 

A    person    is    always    well    F\S.  152.    section  of  a  tooth. 


entine 


Pulp 
Cavity 


Blood 
Vessel 


Cement 


Nerve 


316  A  YEAR  IN  SCIENCE 

repaid  for  any  care  he  may  give  his  teeth.  They  should 
be  carefully  brushed  at  least  twice  a  day.  It  is  well 
occasionally  to  use  a  soft  powder.  A  mild  antiseptic 
mouth  wash  is  also  beneficial.  The  teeth  should  be 
inspected  by  a  dentist  once  or  twice  a  year. 

The  tongue.  The  tongue  is  a  muscular  organ 
attached  at  the  back  to  the  floor  of  the  mouth.  On  its 

upper  surface  are  .numerous 
elevations  of  different  sizes. 
These  are  called  papillae ;  in 
them  are  located  the  nerves  of 
taste.  In  what  form  must  a 
substance  be  in  order  to  taste 
it? 

Salivary  glands.     In   the 
mouth  there  are  two  secre- 

Fig.  153.     The  tongue.  ,.  «  ,, 

membrane,  and  saliva  from  the  salivary  glands.  There 
are  three  pairs  of  salivary  glands.  Two  of  these 
glands,  the  parotid  (Greek  meaning,  "beside  the  ear") 
are  located  in  front  of  and  below  the  ear.  These  are 
the  glands  which  swell  in  the  disease  known  as  the 
mumps.  From  the  parotid  gland  on  each  side  a  tube, 
the  duct,  opens  on  the  inside  of  the  cheek  opposite  the 
upper  second  molar  tooth. 

The  other  two  pairs  of  glands  lie  in  the  floor  of  the 
mouth.  These  are  the  sub-maxillary  (Latin,  sub  means 
beneath,  and  maxilla  means  jawbone)  and  the  sub- 
lingual  (Latin,  sub  means  beneath,  and  lingua  means 


DIGESTIVE  SYSTEM  317 

tongue).  The  ducts  from  these  glands  open  in  the 
floor  of  the  mouth  just  below  and  back  of  the  lower 
incisor  teeth. 

Throat  or  pharynx.  This  is  a  small  cone-shaped 
cavity  just  back  of  the  mouth  cavity.  On  each  side 
of  the  throat  there  is  an  almond-shaped  gland,  the  tons-il. 
There  are  seven  openings  in  the  throat:  two  at  the 
top  open  into  the  nasal  cavity,  one  into  the  mouth,  one 
into  the  esophagus,  one  into  the  wind  pipe,  and  one  into 
each  ear.  The  tubes  leading  to  the  ears  are  known  as 
the  Eustachian  tubes.  The  wind  pipe  lies  in  front  of 
(or  ventral  to)  the  gullet.  At  the  top  of  the  wind  pipe 
is  the  voice  box.  This  can  be  closed  by  a  small  trap 
door  called  the  epiglottis. 

Esophagus.  The  esophagus  is  a  narrow  tube  about 
nine  inches  long  leading  from  the  throat  to  the  stomach. 
Just  before  it  reaches  the  stomach  it  passes  through  a 
sheet  of  muscle  and  connective  tissue  known  as  the 
diaphragm.  This  muscular  partition  divides  the  body 
into  an  upper  portion,  the  thorax,  and  a  lower  portion, 
the  abdomen. 

Stomach.  The  stomach  lies  in  the  middle  of  the  body 
just  below  the  diaphragm.  It  is  a  muscular  organ, 
more  or  less  pear-shaped  with  the  larger  end  lying  toward 
the  left  side.  When  moderately  filled,  it  holds  about 
three  pints.  The  small  end  of  the  stomach  is  con- 
tinuous with  the  intestine.  The  opening  into  the  small 
intestine  is  controlled  by  a  ring  of  muscle.  The  con- 
traction of  this  muscle  closes  the  opening  and  prevents 


318  A  YEAR  IN  SCIENCE 

the  food  from  passing  out  of  the  stomach  as  soon  as  it 
enters. 

The  stomach  is  lined  with  a  mucous  membrane.  This 
is  larger  than  the  stomach  and  is  thrown  into  folds 
running  lengthwise  of  the  organ.  When  examined  with 
a  lens,  this  membrane  is  seen  to  be  covered  with 
numerous  small  pits,  which  are  the  openings  of  many 
little  tubes  formed  by  the  folding  of  the  mucous  mem- 
brane. This  further  increases  the  internal  surface  of 
the  stomach.  Each  tube  is  the  outlet  of  a  gastric  gland. 
These  glands  secrete  another  digestive  fluid,  the  gastric 
juice. 

Intestines.  The  intestines  are  divided  into  two 
regions.  The  first,  a  tube  about  twenty  feet  long  and 
with  a  diameter  varying  from  two  inches  near  the 
stomach  to  one  inch  at  the  other  end,  is  called  the 
small  intestine.  The  second,  the  large  intestine,  is  about 
five  feet  long  with  a  diameter  varying  from  two  and 
one-half  to  one  and  one-half  inches.  The  general 
arrangement  of  the  two  intestines  is  shown  in  the  figure. 
Notice  how  the  small  intestine  enters  the  large  one. 
Projecting  from  the  sack-like  pouch  at  the  beginning 
of  the  large  intestine  is  a  worm-like  extension,  the 
vermiform  appendix.  Inflammation  of  the  appendix 
causes  the  disease  known  as  appendicitis. 

The  small  intestine,  like  the  stomach,  is  lined  by  a 
mucous  membrane  which  is  thrown  into  folds  across 
the  tube.  The  surface  of  the  mucous  membrane  is 


DIGESTIVE  SYSTEM  319 

further  increased  by  numerous  minute  projections 
called  villi. 

As  before  stated,  the  secretions  from  three  kinds 
of  glands  are  poured  into  the  small  intestine.  The 
intestinal  glands  are  embedded  in  the  Avails  of  the 
intestine.  The  other  two  glands  are  the  liver  and  the 
pancreas. 

Liver.  The  liver  is  the  largest  gland  in  the  body.  It 
is  a  dark  red  mass  and  lies  just  under  the  diaphragm. 
On  the  inner  side  of  it  is  located  a  small  sac,  the  gall 
bladder.  In  this  the  bile,  secreted  by  the  liver,  is 
stored  until  it  is  needed.  The  duct  from  the  liver  enters 
the  small  intestine  just  below  the  stomach. 

Pancreas.  The  pancreas,  often  called  sweet  breads, 
lies  just  below  the  stomach.  It  secretes  a  digestive  fluid 
called  the  pancreatic  juice.  This  enters  the  intestine 
through  the  same  duct  as  the  bile. 

Peritoneum  and  mesentery.  Lining  the  abdominal 
cavity  there  is  a  thin  moist  membrane,  the  peritoneum. 
From  the  back  it  folds  over  the  organs  of  the  abdomen 
and  forms  their  outer  covering.  The  stomach  and  the 
twenty-five  or  thirty  feet  of  intestines  are  suspended  by 
a  double  fold  of  peritoneum.  This  is  known  as  the 
mesentery  and  is  attached  to  the  body  wall  in  the  upper 
part  of  the  abdominal  cavity.  The  organs  hang  loosely 
suspended  in  this  cavity.  The  manner  of  their  suspen- 
sion and  their  smooth  outer  covering  give  the  loops  of 
the  intestines  perfect  freedom  of  motion  on  each  other. 


320  A  YEAR  IN  SCIENCE 

Questions 

1.  Name  the  contents  of  the  thoracic  cavity. 

2.  What    organs    are    located    in    the    abdominal 
cavity  ? 

3.  Name  and  locate  the  parts  of  the  alimentary 
canal. 

4.  Give  eight  facts  concerning  an  adult's  teeth. 

5.  What  is  the  appearance  of  the  upper  surface 
of  the  tongue? 

6.  Name  the  seven  openings  in  the  pharynx. 

7.  What  is  the  diaphragm? 

8.  Locate  the  stomach.    What  is  its  size? 

9.  Compare  the  small  and  large  intestines  in  size. 

10.  Locate  the   appendix.     What  is  the   cause   of 
appendicitis  ? 

11.  Name  and  locate  the  salivary  glands,   gastric 
glands,  liver,  pancreas,  and  intestinal  glands. 

12.  Which  of  the  digestive  glands  is  the  largest  ? 


CHAPTER  XXXIX 

DIGESTION 

Introduction.  The  alimentary  canal  is  a  series  of 
small  chemical  laboratories,  in  each  of  which  are  special 
digestive  fluids.  These  are  chemicals  which  act,  each  in 
a  special  way,  upon  the  foods  with  which  they  come  in 
contact.  This  whole  process  we  call  digestion. 

Necessity  of  digestion.  We 
have  learned  in  our  labora- 
tory exercises  that  if  molasses 
and  water  are  separated  by 
an  animal  membrane,  diffu- 
sion takes  place  in  both  direc- 
tions. We  did  not  learn, 
however,  that  all  liquids 
would  not  behave  in  this  man- 
ner. If  we  used  olive  oil  or 
the  white  of  egg,  the  results 
would  be  very  different. 
Neither  the  egg  nor  the  oil 
would  diffuse. 

In    order    that    the    food 
which  we  eat  may  be  utilized,   it   must  leave  the  ali- 
mentary canal  and  be  taken  to  all  parts  of  the  body 

321 


Fig.  154.  Experiment  show- 
ing diffusion.  The  liquid  in 
the  thistle  tube  is  separated 
from  that  in  the  jar  by  an 
animal  membrane. 


322  A  YEAR  IN  SCIENCE 

by  the  blood.  The  walls  of  the  alimentary  canal  have 
no  openings,  neither  have  the  walls  of  the  blood  vessels. 
Consequently  the  food  must  pass  through  these  walls 
by  diffusion.  Obviously,  then,  the  purpose  of  the  process 
of  digestion  is  to  act  upon  the  food  in  such  a  way  that 
it  can  diffuse  through  these  membranes.  This  means 
that  it  must  be  not  only  in  the  form  of  a  liquid  but  in 
the  form  of  particular  kinds  of  liquids,  for  all  liquids 
do  not  diffuse. 

Action  upon  food.  In  its  passage  through  the  canal, 
food  is  acted  upon  both  physically  and  chemically. 
The  food  is  chewed  or  rubbed  into  small  fragments. 
If  soluble,  these  then  dissolve.  If  they  can  not  be  disr 
solved,  they  then  undergo  chemical  changes  which 
make  them  soluble  and  simpler  in  their  composition. 
This  action  is  brought  about  by  substances  in-  the 
digestive  juices  called  enzymes. 

Digestion  in  mouth.  When  the  food  enters  the 
mouth  it  is  first  chewed  or  masticated.  This  enables 
us  to  swallow  it  more  easily.  But,  of  far  greater 
importance  is  the  fact  that  by  breaking  the  food  up 
into  small  particles  we  expose  more  of  it  to  the  action 
of  the  digestive  juices.  It  is  very  important  that  we 
chew  our  food  thoroughly.  "In  chewing,  the  food  is 
moved  about  largely  by  the  action  of  the  tongue.  At 
the  same  time,  it  is  mixed  with  the  liquid  in  the 
mouth,  which  is  a  mixture  of  mucus  and  saliva. 

Saliva  is  a  slightly  alkaline  liquid,  mainly  water.  By 
jt  the  food  is  moistened  and  softened ;  at  the  same  time 


DIGESTION  323 

sugar,  salt,  and  a  few  other  substances  are  dissolved. 
Chemically,  saliva  acts  upon  starch,  changing  it  into  a 
form  of  sugar.  Only  a  small  part  of  the  starch  which 
we  eat  has  time  to  be  changed  during  the  short  time 
the  food  is  in  the  mouth.  The  food  is  pushed  back 
from  the  mouth  by  the  tongue.  It  passes  down  the 
esophagus  and  enters  the  stomach. 

Digestion  in  stomach.  The  walls  of  the  stomach  are 
composed  of  several  layers  of  muscles.  By  the  action 
of  these  muscles  the  food  is  churned  about  and  thus 
thoroughly  mixed  with  the  gastric  juice.  The  stomach 
may  be  closed  by  means  of  the  ring  of  muscles  at  the 
lower  end.  At  intervals  it  is  opened  to  allow  the  food 
which  is  suitably  prepared  to  pass  on. 

Gastric  juice  is  a  thin  colorless  liquid  consisting 
mainly  of  water  (99.4%).  In  it  are  also  small  amounts 
of  hydrochloric  acid  and  two  enzymes,  pepsin  and 
rennin.  The  pepsin  and  hydrochloric  acid  act  upon 
proteins.  As  a  result  of  this  action,  protein  is  ready 
for  diffusion.  Eennin  acts  only  upon  the  protein  of 
milk.  This  it  curdles,  after  which  the  protein  is  acted 
upon  by  the  pepsin.  Rennin  is  frequently  used  in  the 
manufacture  of  cheese.  In  the  stomach  fats  are  melted 
and  oils  are  emulsified;  that  is,  they  are  broken  up  into 
very  small  drops  and  then  scattered  through  the  fluid. 

The  food  remains  in  the  stomach  about  three  hours. 
The  gastric  juice  starts  to  flow  when  food  enters  the 
stomach.  The  flow  may  be  further  stimulated  by  the 
flavor  of  food.  It  has  been  estimated  that  about  three 


324  A  YEAR  IN  SCIENCE 

quarts  of  gastric  juice  are  formed  in  twenty-four 
hours. 

Digestion  in  intestine.  The  food  as  it  enters  the  small 
intestine  is  composed  of  very  fine  particles  mixed  with 
much  fluid.  These  particles  are  partly  digested.  Aside 
from  the  mechanical  action  on  the  food,  part  of  the 
starch  has  been  changed  to  sugar  in  the  mouth,  and 
protein  has  been  partly  digested  in  the  stomach.  The 
remainder  of  the  starch  and  protein  and  all  of  the 
fats  need  now  to  be  acted  upon  by  the  three  digestive 
juices  in  the  small  intestine.  These  juices  are  all 
alkaline. 

The  intestinal  juice  acts  upon  starch,  changing  it  to 
sugar.  It  also  acts  upon  all  the  complex  sugars,  reduc- 
ing them  to  sugars  of  very  simple  composition. 

Bile  assists  in  the  digestion  of  fats.  The  pancreatic 
juice,  the  most  important  of  the  digestive  juices,  acts 
upon  all  kinds  of  foods.  It  contains  one  enzyme  which 
acts  on  starches  and  sugars,  another  which  acts  on 
proteins,  and  still  another  which  converts  some  of  the 
fat  into  soap,  fatty  acids,  and  glycerine. 

By  the  action  of  the  muscles  in  the  walls  of  the 
intestine  the  food  is  slowly  moved  along  in  the  small 
intestine.  At  the  same  time  that  the  undigested  food  is 
being  acted  upon,  the  digested  food  is  being  diffused  into 
the  blood.  It  probably  requires  seven  or  eight  hours  for 
food  to  pass  the  length  of  the  small  intestine. 

Large  intestine.  The  food  passes  very  slowly 
through  the  large  intestine.  There  are  no  new  digestive 


DIGESTION  395 

juices  added  to  the  foods,  but  those  already  mixed 
with  the  food  continue  their  action,  diffusion  goes  on, 
and  finally  there  are  left  in  the  large  intestine  only 
such  substances  as  can  not  be  digested.  These  sub- 
stances, known  as  the  feces,  consist  chiefly  of  woody 
parts  of  cell  walls  of  vegetables,  hard  tough  parts  of 
meats,  and  brown  colored  Avaste  from  the  bile. 

It  is  very  necessary  that  these  waste  products  be 
regularly  expelled  from  the  body.  In  them  the  con- 
ditions are  excellent  for  the  growth  of  bacteria,  which 
result  in  the  formation  of  poisons.  These  poisons,  if 
allowed  to  accumulate,  may  become  absorbed  and  cause 
headaches  followed  by  more  serious  effects.  Proper 
exercise  and  a  suitable  diet,  including  fruits,  large 
amounts  of  water,  and  much  coarse  food  will  aid  greatly 
in  preventing  clogging  of  the  intestines. 


Fig.    155.      A    small    portion    of    the    wall    of    the    small    intestine 
magnified  to  show  the  villi. 

Absorption.  As  we  have  stated  before,  the  chief 
purpose  of  the  process  of  digestion  is  to  prepare  the 
food  so  that  it  will  diffuse.  This  process  of  diffusion 


326 


A  YEAR  IN  SCIENCE 


Epithelium 


in  the  alimentary  canal  is  commonly  known  as 
absorption.  By  means  of  folds  and  finger-like  pro- 
jections, villi,  the  lining-  of  the  small  intestine  is 

especially  adapted  for 
absorption.  In  each 
villus  there  are  two  sets 
of  small  vessels.  One 
set  contains  blood,  the 
other  contains  a  watery 
fluid  called  lymph. 

The  sugars  and  nitrog- 
enous foods  pass  into 
the  blood  vessels  and 
are  then  carried  into 
larger  vessels  through 
the  liver,  and  from  there 
to  the  heart.  In  passing 
through  the  liver  some  of  the  sugar  is  left  behind  and 
stored  in  the  form  of  glycogen  or  "liver  starch."  Fats 
pass  into  the  lymph  vessels.  These  enter  larger  vessels 
which  finally  empty  into  a  vein  in  the  neck.  From 
there  the  fats  enter  the  heart  with  the  blood.  From  the 
heart  all  these  foodstuffs  are  then  distributed  to  all 
parts  of  the  body. 

Questions 

1.  Explain  fully  why  it  is  necessary  to  have  the 
food  digested. 

2.  What  is  an  enzyme? 


Fig.   156.      Section    of    a    villus, 
highly    magnified. 


DIGESTION  3*27 

3.  What    changes,    physical    and    chemical,    take 
place  in  the  food  while  it  is  in  the  mouth? 

4.  What   is   the   digestive  fluid  in  the   stomach? 
What  chemical  change  does  it  produce  in  the  food'? 

5.  Name   the  three   digestive  fluids  in  the  small 
intestine. 

6.  State   definitely   the   action  of  each  upon   the 
food. 

7.  In  what  part  of  the  alimentary  canal  does  most 
food  diffuse  into  the  blood? 

8.  What  is  the  structure  of  a  villus? 

9.  Trace  the  path  taken  by  fats  from  the  intestine 
to  the  heart. 

10.  Trace  sugars  and  proteins  from  the  intestine 
to  the  heart. 

11.  Which  foodstuff  is  stored  in  the  liver? 

12.  How  long  does  it  take,  from  the  time  food  is 
eaten,  until  it  becomes  a  part  of  the  body? 

13.  What  is  the  function  of  the  large  intestine  ? 


CHAPTER  XL 

NARCOTICS  AND  STIMULANTS 

Characteristics.  Narcotics  are  substances  which 
decrease  the  activity  of  the  brain.  If  taken  in  large 
doses,  they  cause  a  person  to  fall  into  a  kind  of  stupor 
or  a  deep  sleep.  The  commonest  narcotics  are  tobacco, 
morphine,  laudanum,  and  opium. 

Stimulants,  on  the  other  hand,  increase  the  activity 
of  the  organs  of  the  body.  Commonly  used  stimulants 
are  alcohol,  tea,  coffee,  strychnine,  and  belladonna. 
Some  of  these,  such  as  alcohol,  act  as  stimulants  in 
moderate  doses  and  when  first  taken  into  the  body.  In 
large  doses  following  this  stimulating  effect,  they 
produce  a  stupor  similar  to  that  resulting  from 
narcotics. 

Neither  narcotics  nor  stimulants  are  necessary  in 
order  that  the  body  may  perform  its  functions  properly. 
Moreover,  it  is  a  well-known  fact  that  persons  who 
have  become  slaves  to  the  use  of  either  are  not  as 
successful  and  happy  as  those  who  do  not  use  them. 

Tobacco.  Tobacco  consists  of  the  dried  leaves  of  the 
tobacco  plant  grown  extensively  in  many  parts  of  the 
south  as  well  as  in  other  warm  climates.  The  active 
substance  in  tobacco  is  nicotine,  a  deadly  poison.  Like 

328 


NARCOTICS  AND  STIMULANTS  329 

other  poisons,  one  may  become  so  accustomed  to  its 
use  by  beginning  with  small  doses,  that  finally  even 
large  doses  produce  little  apparent  effect.  The  nicotine 
is  a  niild  narcotic.  It  dulls  the  sensibilities  and 
weakens  the  nerves.  In  young  boys  who  are  habitual 
users  of  tobacco  the  nervous  system  does  not  develop 
properly.  As  a  result,  they  fall  behind  in  their  school 
work.  Less  than  1%  of  the  school  children  who  smoke 
are  able  to  keep  up  their  work.  They  become  dull  and 
backward  instead  of  keen  and  alert.  They  are  not  apt 
for  school  work.  They  are  often  rejected  for  athletics 
because  they  can  not  act  and  think  quickly.  In  a 
similar  way,  later  in  life  they  are  not  fitted  for  such 
positions  as  demand  good,  clear,  and  rapid  thinking. 

Much  of  the  nicotine  is  absorbed  by  the  blood  vessels 
and  is  then  passed  into  the  heart.  It  has  very  injurious 
effects  upon  this  organ,  especially  in  young  people. 
The  heart  becomes  enlarged  and  weakened  sometimes 
to  such  an  extent  that  a  " tobacco  heart"  is  produced. 
This  frequently  makes  it  necessary  to  reject  boys  from 
athletic  contests  and  from  occupations  requiring  a 
good  physique. 

Many  business  corporations  demanding  workers  who 
are  mentally,  physically,  and  morally  sound  will  not 
employ  a  person  who  is  a  smoker.  This  alone  should 
be  sufficient  argument  against  the  use  of  tobacco. 

Opium  and  other  narcotics.  Opium  is  made  from  the 
milky  juice  which  is  found  in  the  green  seed-pod  of  the 
poppy.  Morphine  and  laudanum  are  made  from  opium. 


330  A  YEAR  IN  SCIENCE 

They  are  all  dangerous  drugs  and  should  not  be  taken 
except  by  the  advice  of  a  physician.  In  medicine  these 
drugs  are  all  valuable,  Because  they  benumb  the 
senses  they  are  frequently  used  to  give  temporary  relief 
to  those  who  are  suffering  intense  pain.  Persons  some- 
times begin  the  use  of  these  drugs  to  relieve  them  of 
pain  or  to  produce  sleep.  In  a  short  time  they  are 
unable  to  stop  taking  them.  Like  other  narcotics  they 
create  an  unnatural  appetite  which  is  only  satisfied  by 
increasingly  larger  doses  of  the  drug  itself.  The  effect 
upon  the  body  is  so  great  that  the  victim  finally  becomes 
a  moral  and  physical  wreck. 

Alcohol.  The  alcohol  used  in  drinks  is  always  pro- 
duced by  the  growth  of  yeast  in  some  liquid  containing 
sugar.  Yeast  is  a  plant.  It  grows  rapidly  and  produces 
a  chemical  action  called  fermentation,  by  which  sugar 
is  changed  to  alcohol  and  carbon  dioxide.  The  alcoholic 
liquors  used  are  prepared  by  different  processes,  but 
all  depend  for  their  stimulating  effect  upon  the  presence 
of  alcohol. 

You  are  already  familiar  with  the  fact  that  many 
persons  who  at  first  use  alcoholic  liquors  in  moderation 
later  become  slaves  to  their  use.  There  is  nothing  more 
deplorable  than  the  sight  of  a  person  who  has  taken 
such  large  quantities  of  alcohol  that  the  activities  of 
the  brain  and  muscles  are  impaired  and  weakened.  He 
does  and  says  things  of  which,  in  his  sober  hours,  he 
is  ashamed.  There  is  no  doubt  of  the  injurious  effects 
of  alcohol  upon  the  body.  Its  effects  are  very  wide- 


NARCOTICS  AND  STIMULANTS  331 

spread.  Excessive  use  of  alcohol  affects  the  liver, 
kidneys,  heart,  blood  vessels,  and  nervous  system. 
More  than  any  other  drug,  it  is  responsible  for  the 
general  break  down  of  the  whole  body. 

Alcohol  not  only  ruins  the  health,  but  it  also  results 
in  much  poverty  and  crime.  A  constant  drinker  spends 
a  large  proportion  of  his  income  for  liquors,  and  at 
the  same  time  he  renders  himself  unfit  to  earn  more 
money.  Wide  and  accurate  scientific  investigations 
have  proved,  beyond  a  doubt,  that  alcohol  is  responsible 
for  a  large  percentage  of  crime.  It  not  only  wrecks 
the  mind,  but  it  wrecks  the  character.  The  cost  of  the 
care  of  the  many,  who,  through  intemperance,  help  to 
fill  up  our  reformatories,  prisons,  and  insane  asylums 
has  been  estimated  at  $100,000,000  annually. 

Conclusion.  After  showing  the  terrible  results  which 
come  from  the  excessive  use  of  narcotics  and  stimu- 
lants, Mr.  Blount*  says:  "We  squander  our  mate- 
rials, waste  our  energies,  and  benumb  our  powers  in 
that  which  harms  but  does  not  satisfy.  And  yet  the 
world  is  full  of  great  things  to  do.  There  are  barren 
lands  to  clothe  with  forest  and  field,  marshes  to  drain, 
canals  to  dig,  works  of  art  to  make,  magnificent  cities 
to  build,  founded  not  on  the  bones  of  the  weak  and 
oppressed,  but  firmly  grounded  in  equality  and  justice. 
This  work  cannot  be  done  by  people  whose  delight  is  in 
tickling  their  senses  with  drugs.  It  is  a  labor  for 

*R.  E.  Blount,  Physiology  and  Hygiene.  Row,  Peterson  and 
Company. 


332  A  YEAR  IN  SCIENCE 

strong  men  and  women.  We  are  summoned  to  mighty 
deeds.  We  must  employ  every  resource  we  have,  use 
every  ounce  of  energy  we  possess,  to  respond  to  the 
call.  We  must  go  into  training,  as  an  athlete  for  a 
contest,  nourish  our  bodies  Avith  the  most  wholesome 
food,  discarding  that  which  is  harmful  or  question- 
able, and  make  us  strong  for  the  conflict.  The  day  of 
heroes  is  not  past.  Choose  a  worthy  object  for  your  life 
work,  put  yourself  in  training  for  it,  and  you  will  have 
nothing  to  fear  from  stimulants  and  narcotics." 

Questions 

1.  What  is  a  narcotic  ?    Name  the  more  commonly 
used  narcotics. 

2.  How  do  stimulants  differ  from  narcotics? 

3.  What  is  the  name  of  the  active  substance  in 
tobacco? 

4.  State  the  principal  reasons  why  boys  who  smoke 
are  often  rejected  for  athletics. 

5.  Are  business  corporations  justified  in  not  em- 
ploying men  who  are  habitual  smokers?     State  the 
reasons  for  your  answer. 

6.  For  what  purposes  are  morphine  and  laudanum 
valuable  ? 

7.  Name    the    organs    of   the    body    upon   which 
alcohol  has  an  injurious  effect. 

8.  Does  any  relation  exist  between  poverty  and 
the  use  of  alcohol? 

9.  To    what    extent    does    alcohol    contribute    to 
crime  ? 

10.     What  is  the  estimated  annual  cost  of  the  care 


NARCOTICS  AND  STIMULANTS  333 

of  those  who  through  intemperance  become  criminals 
or  become  insane? 

11.  In  how  many  states  is  the  sale   of  alcoholic 
liquors  now  prohibited? 

12.  What  are  the  principal  arguments  in  favor  of 
prohibition?     Against  it?    How  do  the  two  compare 
in  number  and  in  value? 

13.  Name  some  of  the  things  which  you  would  like 
to    accomplish    during   your   life.      Will   the    use    of 
tobacco  and  alcohol  assist,  or  hinder,  you  in  the  ful- 
fillment of  these  ambitions? 

14.  What  federal  law  do  we  have  to  regulate  the  sale 
of  morphine,  cocaine,  and  similar  drugs  ? 


CHAPTER  XLI 

CIRCULATORY  SYSTEM 

Introduction.  In  plants  we  learned  that  there  were 
tubes  through  which  liquids  passed  from  one  part  of 
the  plant  to  another.  In  our  bodies  there  are  also 
tubes  through  which,  liquids  are  forced.  These  liquids 
have  two  very  important  functions.  First,  they  carry 
food  from  the  alimentary  canal  and  oxygen  from  the 
lungs  to  all  parts  of  the  body,  so  that  each  part  receives 
what  it  needs.  Second,  they  carry  waste  materials 
from  all  parts  of  the  body  to  the  organs  from  which 
they  can  be  removed. 

The  set  of  organs  which  performs  these  two  func- 
tions is  the  circulatory  system.  This  system  consists  of 
three  parts: 

1.  Blood   and  lymph,  liquids  which  floAV  through 
tubes. 

2.  The  heart,  a  pump  for  forcing  the  blood  around. 

3.  Blood  and  lymph  vessels. 

Blood.  The  liquid  which  flows  through  the  blood 
vessels  we  call  blood.  It  consists  of  a  watery  fluid  called 
plasma.  Floating  in  this  are  very  small  cells  called 
corpuscles.  There  are  three  kinds  of  these  cells:  red 
corpuscles,  white  corpuscles,  and  blood  plates.  The  last 

334 


CIRCULATORY  SYSTEM  335 

of  these  disintegrate  so  rapidly  when  blood  is  removed 
from  the  body  that  very  little  is  known  of  their  structure. 
The  plasma  of  the  blood  is  largely  water  and  is  almost 
colorless.  The  red  color  of  the  blood  is  due  to  the  red 
corpuscles  which  float  in  it.  It  contains,  however,  all  the 
food  and  waste  products  which  are  soluble.  This  food  is 
carried  to  all  the  cells  of  the  body,  and  the  waste  products 
are  taken  to  the  excretory  organs.  The  composition  of 
the  plasma  thus  varies  greatly  in  different  parts  of  the 
body.  The  plasma  diffuses  readily  through  the  walls  of 
the  blood  vessels  and  thus  comes  directly  in  contact  with 
the  body  cells.  As  soon  as  the  plasma  has  left  the  blood 
vessels  it  is  called  lymph. 

Lymph.  Lymph  is  blood  plasma,  minus -the  red  cor- 
puscles. It  is  a  colorless  liquid  in  which  all  the  tissues 
are  bathed.  The  watery  fluid  which  collects  in  a  water 
blister  is  lymph.  From  this  lymph  the  body  cells  take 
such  food  substances  as  they  need.  In  exchange  they 
return  to  the  lymph  waste  products  formed  as  a  result 
of  the  action  of  the  cells.  Part  of  this  lymph  filled 
with  waste  products  again  diffuses  directly  into  the  blood. 
The  rest  is  collected  into  lymph  vessels,  which  we  have 
learned  finally  enter  the  blood  vessels. 

Red  corpuscles.  When  a  drop  of  blood  is  examined 
under  a  microscope,  the  red  corpuscles  appear  as  small 
disk-shaped  cells  of  a  reddish  yellow  color.  A  corpuscle 
is  round  and  flat  like  a  coin,  but  thinner  in  the  middle 
than  near  the  edge.  They  are  all  about  the  same  size, 
about  1/3,500  of  an  inch  in  diameter.  They  are  so 


336 


A  YEAK  IN  SCIENCE 


numerous  that  between  four  and  five  million  are  present 
in  one  cubic  millimeter  of  blood.  Like  other  cells  they 
are  composed  of  protoplasm.  They  likewise  wrear  out 

and  must  be  replaced. 
Some  are  produced 
by  the  cells  in  the  red 
marrow  of  bones. 
The  color  of  the  cor- 
puscles is  due  to  the 

presence    of    a    sub- 
Fig.  157.     Blood  corpuscles;  A,  red      0fQr,rt0     V  n  r\  -or  n      QC 
corpuscles    from    above;    B,    from    the      Stance      Known      as 
side ;  C,  in  chains  ;  D,  white  corpuscles.  .  _ 

hemoglobin.  By 

means  of  this  the  corpuscle  can  perform  its  important 
function  of  -carrying  oxygen. 

When  the  blood  passes  through  the  small  blood 
vessels  into  the  lungs,  oxygen  from  the  air  in  the 
lungs  is  diffused  into  it.  The  hemoglobin  then  combines 
chemically  with  the  oxygen  and  forms  an  oxide  of 
hemoglobin.  As  the  blood  circulates  through  the  body, 
the  oxygen  is  given  up  to  the  cells  of  the  body  where 
it  is  needed.  At  the  same  time  the  blood  loses  its 
bright  red  color,  which  had  been  due  to  the  presence 
of  the  oxide  of  hemoglobin. 

White  corpuscles.  The  white  bodies  are  not  as 
numerous  as  the  red.  There  is  one  white  to  about 
every  six  hundred  red.  They  are  larger,  colorless,  and 
irregular,  and  change  their  shape  rapidly.  They  are 
not,  as  the  red,  restricted  to  the  blood  vessels.  By  their 
movements  they  can  get  through  the  walls  and  flow 


CIRCULATORY  SYSTEM  337 

out  into  the  tissues.  They  are  always  found  in  large 
numbers  in  the  region  of  wounds.  Here  they  may  aid 
in  repairing  the  injured  part,  but  they  are  most  useful 
in  destroying  the  many  bacteria  which  collect  about 
wounds.  This  they  do  by  flowing  around  the  bacteria 
and  then  by  digesting  them. 

Coagulation.  When  blood  escapes  from  the  blood 
vessels  into  the  tissues,  or  when  a  vessel  is  ruptured 
and  it  escapes  from  the  body,  it  soon  coagulates  or  clots. 
This  process  is  the  result  of  the  action  of  an  enzyme. 
The  function  of  clotting  is  to  plug  up  the  wound  and 
so  prevent  excessive  bleeding. 

Amount  of  blood.  The  blood  constitutes  about  one- 
thirteenth  of  the  weight  of  the  "body.  The  distribution 
of  this  to  the  parts  of  the  body  varies  at  different  times. 
Just  after  a  meal  more  blood  is  needed  in  the  digestive 
organs.  During  exercise  more  blood  is  sent  to  the 
working  muscles. 

The  amount  of  blood  going  to  all  parts  of  the  body 
depends  upon  the  rate  of  the  heart  beat.  The  amount 
sent  to  each  organ,  however,  can  not  be  regulated  by 
the  heart.  This  regulation  is  brought  about  by  a 
change  in  the  diameter  of  the  blood  vessels  leading 
to  or  from  the  organ  in  question.  If  more  blood  is 
needed  in  the  stoma.ch,  for  example,  the  diameter  of 
the  blood  vessel  going  to  the  stomach  is  enlarged. 
This  is  the  result  of  the  action  of  the  muscles  in  its 
wall,  which  is  controlled  in  turn  by  the  nervous 
system.  There  is  less  resistance  to  the  flow  of  blood 


338 


A  YEAR  IN  SCIENCE 


in  a  large  vessel  than  there  is  in  a  small  one,  conse- 
quently more  blood  enters  it. 

The  heart  structure.  The  heart  is  a  conical  shaped 
organ  about  the  size  of  a  man's  fist.  It  lies  in  the  chest 
cavity  just  above  the  diaphragm  and  directly  back  of 
the  lower  two-thirds  of  the  breast  bone.  The  apex  is 
below  and  slightly  to  the  left  of  the  breast  bone,  where 

its  beat  can  easily 
be  felt  between  the 
ribs.  The  heart  is 
enclosed  in  a  sac 
called  the  pericar- 
dium. Between  this 
and  the  heart  there  is 
a  fluid  which  lessens 
the  friction  caused  by 
the  beating  of  the 
heart. 

Since  the  heart  is 
a  pump,  we  naturally 
expect  that  it  is  made 
of  muscle.  Inter- 
nally the  heart  is 

Fig.  158.     External  view  of  the  heart,      divided      into      f  O  U  r 

cavities;  the  upper  two  called  the  auricles,  the  lower 
two  the  ventricles.  The  ventricles  are  larger  than 
the  auricles  and  have  much  thicker  walls.  There 
are  no  openings  between  the  left  and  the  right  sides 
of  the  heart,  but  there  is  an  opening  between  the  left 


CIRCULATORY  SYSTEM 


339 


auricle  and  ventricle  and  between  the  right  auricle  and 
ventricle.  Each  of  these  openings  is  guarded  by  a 
valve.  These  are  so  arranged  that  when  they  are  closed 
no  blood  can  pass  from  the  ventricles  back  into  the 

auricles. 


Pulmonary 


Superior 
Vena  Cava 


Right  - 
Auricle 


Right 
,'entric 


Fig.  159.     Diagram  to  show  the  internal  structure  of  the  heart. 

Connected  with  the  heart  are  tubes  called  blood 
vessels.  The  tubes  which  carry  blood  to  the  heart  enter 
the  auricles  and  are  known  as  veins.  Those  vessels 
through  which  blood  leaves  the  heart  from  the  ventricles 
are  called  arteries. 


340  A  YEAR  IN  SCIENCE 

Action  of  heart.  The  left  and  right  sides  of  the  heart 
Avork  in  unison.  However,  for  convenience,  we  will 
follow  the  flow  of  the  blood  through  one  side  of  the 
heart  and  then  through  the  other.  Blood  enters  the 
right  auricle  through  two  large  veins.  One,  the 
superior  vena,  brings  blood  from  the  upper  part  of  the 
body;  the  other,  the  inferior  vena,  carries  blood  from, 
the  lower  part  of  the  body.  From  the  right  auricle 
the  blood  enters  the  right  ventricle.  Then  it  is  forced 
into  a  large  artery,  the  pulmonary  artery,  which  takes 
it  to  the  lungs  where  the  blood  receives  a  new  supply  of 
oxygen  and  loses  carbon  dioxide.  It  returns  to  the 
left  auricle  through  four  pulmonary  veins,  and  then 
enters  the  left  ventricle  from  which  it  is  forced  to  all 
parts  of  the  body  through  the  aorta. 
.  To  the  cells  of  the  body  it  furnishes  food  and  oxygen. 
Into  it  they  return  waste  products,  carbon  dioxide, 
water,  and  nitrogenous  substances.  With  the  exception 
of  carbon  dioxide,  most  of  these  waste  products  are 
removed  from  the  veins  before  the  blood  again  returns 
to  the  heart  through  the  vena  cavas. 

There  are  two  sets  of  valves  in  the  heart.  One  set, 
already  referred  to,  prevents  the  blood  from  the  ven- 
tricles returning  to  the  auricles.  The  other  valves  are 
found  one  in  each  artery.  These  prevent  the  blood  in 
the  arteries  from  returning  to  the  ventricles. 

Beat.  A  beat  of  the  heart  is  the  contraction  of  the 
walls  of  the  auricles  and  of  the  ventricles.  The  two 
auricles  contract  at  the  same  time;  then  the  two  ven- 


CIRCULATORY  SYSTEM 


341 


tricles;  and  then  there  is  a  pause.  This  is  followed 
immediately  by  another  contraction  of  the  auricles. 
The  heart  beats  in  an  adult  about  seventy  two  times  a 
minute,  but  its  rate  varies  in  different  individuals. 


Capillaries 
Lungs 


Pulmona 
Artery 


Vena  Ca 


Capillaries 
of  Body 


Pulmonary 
Vein 


\-Aorta 


Fig.    160. 


Diagrammatic   representation    of   the   circulation    of   the 
blood. 


The  structure  of  the  heart  is  such  that  the  blood 
passes  into  the  ventricles.  The  thick  walls  of  the 
ventricles  then  contract  and  force  the  blood  out  into 
the  arteries.  While  the  ventricles  are  contracting 


342  A  YEAR  IN  SCIENCE 

they  can  not  receive  more  blood.  During  this  time 
blood  is  entering  the  auricles  which  serve  as  reservoirs. 
Blood  and  lymph  vessels.  When  the  heart  beats,  the 
blood  is  forced  with  considerable  pressure  into  vessels 
which  we  have  called  arteries.  In  order  to  withstand 
this  pressure,  arteries  must  have  thick,  elastic  walls. 
After  the  blood  has  passed  through  the  arteries  and 
before  the  heart  beats  again,  the  arteries  spring  back 
to  their  normal  size. 


Vein.  Artery 

Fig.   161.     Cross  section  of  an  artery  and  of  a  vein. 

Arteries  generally  are  not  near  the  surface  of  the 
body.  In  a  few  places,  however,  such  as  the  wrist,  the 
temples,  and  on  the  under  side  of  the  knees  arteries 
are  near  enough  the  surface  so  that  the  expansion  of 
their  walls  following  each  heart  beat  can  be  felt.  This 
we  call  the  pulse.  If  we  trace  the  arteries  away  from 
the  heart,  we  find  that  each  one  divides  and  subdivides 
a  great  many  times  so  that  gradually  the  branches  become 
smaller  and  smaller.  At  the  same  time  the  walls 
become  thinner.  Finally  very  small  tubes  with  very 
thin  walls  are  left,  called  capillaries.  We  can  not  prick 
any  spot  on  the  skin  with  a  needle  without  causing 


CIRCULATORY  SYSTEM  343 

bleeding.  Evidently  the  skin  is  filled  with  these  small 
capillaries,  so  small  that  they  can  not  be  seen  with  the 
naked  eye.  The  estimated  diameter  of  these  vessels 
is  1/3,000  of  an  inch. 

If  we  continue  to  trace  the  capillaries,  WQ  notice  that 
gradually  they  unite  to  form  larger  tubes  with  thicker 
walls.  These  tubes  become  successively  larger  and 
finally  form  the  large  veins  which  enter  the  heart. 
The  walls  of  veins  are  thinner  than  those  of  the 
arteries,  but  they  will  not,  like  arteries,  remain  dis- 
tended when  there  is  no  blood  in  them.  The  blood 
pressure  in  veins  is  low.  In  order  to  prevent  the 
backward  flow  of  blood  many  of  the  veins  are  supplied 
with  pocket-like  valves.  These  valves  open  and  thus 
close  the  vein  if  the  blood  tends  to  flow  back  toward 
the  capillaries. 

Lymph  vessels.  The  veins  are  assisted  in  returning 
the  blood  to  the  heart  by  a  set  of  tubes  known  as  the 
lymph  vessels.  These  vessels  originate  in  the  (lymph) 
intercellular  spaces  in  the  tissues.  They  gradually  run 
together  to  form  larger  vessels  and  finally  empty  their 
contents  into  the  veins  at  the  sides  of  the  neck. . 


Questions 

1.  State  the  chief  uses  of  the  circulatory  system. 

2.  What  are  the  three  parts  of  this  system? 

3.  What  is  the  composition  of  blood  plasma?    Its 

use? 


344  A  YEAR  IN  SCIENCE 

4.  Contrast  the  red  and  the  white  blood  corpuscles 
as  to  si^e,  appearance,  number,  and  use  in  the  body. 

5.  What  is  hemoglobin? 

6.  HOAV  is  the  amount  of  blood  which  goes  to  each 
organ  regulated? 

7.  Why  is  it  difficult  to  study  immediately  after 
eating  ? 

8.  Describe  the  internal  structure  of  the  heart. 

9.  Locate  and  give  the  function  of  the  superior 
vena    cava,    the    inferior    vena    cava,    the    pulmonary 
artery,  the  pulmonary  vein,  and  the  aorta. 

10.  Trace  a  drop  of  blood  from  the  left  ventricle 
throughout  the  body  and  back  to  the  left  ventricle. 

11.  How    many    times    does    the    heart    beat    per 
minute? 

12.  What  is  the  advantage  in  having  the  walls  of 
the  left  side  of  the  heart  thicker  than  those  of  the 
right? 

13.  What  is  the  function  of  the  pericardium,  the 
auricles,  and  the  ventricles? 

14.  What  is  the  pulse?     Locate  three  places  in  the 
body  where  a  pulse  may  be  felt. 

15.  Give  three  ways  in  which  arteries  differ  from 
veins. 

16.  What  are  capillaries  ?    Show  by  a  diagram  their 
relation  to  arteries  and  veins. 

17.  Give  some  first  aid  suggestions  for  the  care  of 
a  cut  vein.    For  the  care  of  a  cut  artery. 

T8.     What  is  lymph?    What  is  its  function? 
19.     How    does    lymph    get    back    into    the    blood 
circulation  ? 


CHAPTER  XLII 

RESPIRATORY  SYSTEM 

Need  of  air.  We  already  know  that  we  must  have 
air  in  order  to  live.  If  a  man  is  shut  off  from  a  supply 
of  air  for  even  a  relatively  short  time  he  dies.  More- 
over, we  constantly  need  a  large  amount  of  air.  From 
fifteen  to  eighteen  times  every  minute  each  one  of  us 
is  taking  in  a  new  supply  of  air  by  a  process  which 
we  call  inhaling.  Each  time  this  is  followed  by  exhaling, 
in  which  air  is  given  off  from  the  body.  The  rate  at 
which  we  breathe  varies.  If  we  are  exercising  we 
breathe  faster  than  we  do  wrhen  at  rest. 

Oxidation.  The  element  in  the  air  essential  for  our 
bodies  is  oxygen.  This  we  know  combines  readily 
with  other  elements,  and  in  so  doing  produces  energy 
in  the  form  of  light  or  heat.  It  is  precisely  this 
property  of  oxygen  which  makes  it  so  necessary  to  the 
cells  in  our  body.  In  order  to  move,  to  think,  and  to 
keep  the  body  warm,  we  must  have  energy.  This  is 
produced  by  the  oxidation  of  the  cells  of  the  body.  As 
a  result  of  oxidation,  waste  products,  especially  carbon 
dioxide,  water,  and  nitrogenous  waste  in  the  form  of 
urea,  are  formed. 

345 


346  A  YEAR  IN  SCIENCE 

Internal  and  external  respiration.  The  process  in 
which  the  cells  of  the  body  take  oxygen  from  the 
blood,  use  it  for  oxidation,  and  return  to  the  blood 
waste  products  is  the  essential  part  of  respiration  and 
is  known  as  internal  respiration.  This  name  distin- 


Lwy*. 


Fig.    162.      The    respiratory   organs. 

guishes  it  from  external  respiration,  which  is  purely  a 
mechanical  process  by  means  of  which  air  is  taken  into 
and  given  off  from  the  body. 


RESPIRATORY  SYSTEM 


347 


Organs  of  respiration.  In  the  digestive  system  food 
is  taken  into  the  alimentary  canal  and  from  there  is 
carried  to  all  parts  of  the  body  by  the  blood.  In  a 
similar  manner,  in  the  respiratory  system  air  is  taken 


Esophagus 


Fig.  163.     Median  section  through  the  head  showing  the  relation  of 
the  mouth  and  nasal  cavities  to  the  esophagus. 


into  the  organs,  called  the  lungs,  and  from  there  it  is 
carried  by  the  blood  to  all  parts  of  the  body. 

Air  enters  the  body  through  the  two  nostrils.  It  then 
passes  backward  into  the  throat,  from  which  it  enters 
the  wind  pipe,  or  trachea,  through  a  slit-like  opening, 
the  glottis.  Just  above  the  level  of  the  heart  the  trachea 


348  A  YEAR  IN  SCIENCE 

divides  into  two  tubes,  the  right  and  the  left"  bronchus, 
each  of  which  supplies  one  lung. 

Nose  cavity.  The  nose  cavity  is  an  irregular-shaped 
passage  lined  with  a  mucous  membrane.  This  secretes 
mucus  which  aids  in  catching  any  dust  and  germs 
which  escape  the  many  fine  hairs  at  the  entrance  of 
the  cavity.  The  air  in  passing  through  the  nose  under- 
goes several  changes;  first,  it  is  partly  freed  of  par- 
ticles of  dust  and  germs;  second,  it  is  warmed;  and 
third,  it  becomes  moist.  Air  may  reach  the  lungs 
through  the  mouth,  but  the  mouth  is  not  adapted  for 
the  purpose.  Mouth  breathing  is  a  habit  to  be 
avoided. 

Larynx.  The  structure  of  the  throat  has  already 
been  studied.  The  air  passes  from  the  throat 
through  the  glottis  into  the  voice  box,  or  larynx.  The 
larynx  is  a  cavity  on  top  of  the  wind  pipe.  Its  walls 
are  stiffened  by  movable  pieces  of  a  substance  known 
as  cartilage.  The  largest  of  these  can  be  felt  on  the 
ventral  side  of  the  larynx,  commonly  called  Adam's 
apple.  Within  the  larynx  are  folds  of  mucous  mem- 
brane. These  folds  form  the  vocal  cords.  When  these 
are  drawn  close  together  and  air  passes  over  them, 
they  vibrate  and  produce  sound.  The  glottis  can  be 
closed  by  the  epiglottis,  as  we  have  previously  men- 
tioned. This  must  be  closed  during  swallowing.  If 
particles  of  food  enter  the  larynx,  choking  results. 

Trachea.  The  trachea,  or  wind  pipe,  is  immediately 
below  the  larynx.  It  and  its  branches  are  kept  open 


RESPIRATORY  SYSTEM  349 

by  incomplete  rings  of  cartilage.  These  can  be  easily 
felt  on  the  ventral  side  of  the  neck.  Attention  has 
already  been  called  to  the  fact  that  the  trachea 
divides  at  the  base  of  the  lungs  into  a  right  and  a  left 
bronchus. 

The  lungs.  Each  bronchus  divides  and  subdivides  a 
great  many  times.  As  these  bronchial  tubes  become 
smaller,  their  walls  become  thinner,  each  tube  ending 
finally  in  a  branching  air  sac  with  extremely  thin  walls 
of  elastic  tissue.  The  walls  of  these  sacs  are  richly 
filled  with  blood  capillaries.  The  bronchial  tubes  and 
air  sacs  are  all  bound  together  with  a  soft,  pink,  elastic 
tissue.  Over  the  whole  is  stretched  an  elastic  mem- 
brane known  as  the  pleura. 

The  pleura.  This  membrane  covers  both  lungs.  At 
the  point  where  the  bronchi  enter  the  lungs  the  pleura 
is  turned  back  and  lines  the  interior  of  the  chest  cavity. 
This  is  another  membrane  which  secretes  a  fluid  to 
reduce  friction.  When  the  lungs  are  filled  with  air 
the  two  layers  of  pleura  rub  against  each  other. 

Mechanism  of  breathing1.  We  are  all  familiar  with 
the  fact  that  certain  movements  of  the  body  accompany 
breathing.  As  a  result  of  those  movements  the  chest 
cavity  is  enlarged.  This  causes  the  air  in  the  lungs  to 
expand ;  in  this  way  the  pressure  is  reduced.  The  greater 
atmospheric  pressure  outside  of  the  body  then  forces 
more  air  into  the  lungs.  Usually  about  one  pint  of  air 
is  taken  in  at  'each  inhalation.  In  exhaling,  the  chest 
again  becomes  smaller.  This  pressure  upon  the  lungs, 


350 


A  YEAR  IN  SCIENCE 


U 


Fig.  164.  Experiment 
to  illustrate  the  effect 
upon  the  lungs  of  the 
movements  of  the  dia- 
phragm. The  belljar  cor- 
responds to  the  walls  of 
the  thorax ;  the  rubber 
balloon  to  the  lungs ;  the 
glass  tube  to  the  trachea ; 
and  the  sheet  of  rubber 
tied  over  the  bottom  of 
the  belljar  to  the  dia- 
phragm. As  the  dia- 
phragm is  lowered  air 
flows  down  the  tube  and 
inflates  jthe  balloon. 


together  with  the  elasticity  of 
their  walls,  is  sufficient  to  force 
out  about  one  pint  of  air. 

The  chest  is  enlarged  by  the 
movements  of  the  diaphragm 
and  of  the  ribs.  Muscles  in  the 
diaphragm  cause  it  to  lower. 
As  a  result,  what  happens  to 
the  abdomen  f  Muscles  between 
the  ribs,  and  between  the  ribs 
and  shoulders,  pull  the  ribs  up 
and  this  movement  pushes  the 
breast  bone  forward.  These 
movements  are  controlled  by 
nerves.  With  effort  we  can 
increase  their  extent  and  so 
inhale  more  air,  and  W3  can 

B  B 


nr 

Fig.  165.  Experiment  showing  movements  of  ribs  in  breathing; 
AB,  vertebral  column ;  CD,  and  EF,  ribs ;  DF}  breast  bone ;  a,  b, 
external  and  internal  intercostal  muscles ;  c,  neck  muscles.  If 
these  muscles  contract,  the  ribs  and  breast  bone  are  drawn  upward. 
This  movement  widens  the  thorax  from  front  to  back  and  from 
side  to  side.  . 

also  forcibly  exhale  more  than  the  usual  amount  of  air. 
It   is   impossible,    however,   to   empty   the   lungs.     The 


RESPIRATORY  SYSTEM 


351 


presence  of  some  air  in  the  lungs  all  the  time  makes  it 
possible  for  the  exchange  of  gases  in  the  blood  to  take 
place  continually  instead  of  at  intervals. 


Rib. 


Fig.  166.     Diagram  showing  the  position  of  the  ribs  and  diaphragm 
in  A,  expiration  ;  B,  inspiration. 

Comparison  of  inhaled  and  exhaled  air.  The  oxygen 
of  the  air  which  is  inhaled  diffuses  through  the  thin 
walls  of  the  air  sacs  and  capillaries  in  the  lungs  and 
enters  the  blood.  Most  of  it  combines  with  the  hemo- 
globin in  the  red  corpuscles  and  is  thus  carried  to  the 
different  cells  of  the  body,  where  it  is  given  up  again. 
As  a  result  of  the  oxidation  which  then  takes  place  the 
energy  which  we  need  is  produced,  and  also,  as  in  any 
burning,  waste  products  are  formed.  Of  these  waste 
products  the  principal  one  removed  by  the  lungs  is 
carbon  dioxide. 


352  A  YEAR  IN  SCIENCE 

A  comparison  of  inhaled  and  exhaled  air  is  most 
readily  appreciated  when  tabulated. 

INHALED                        EXHALED  CHANGE 

Approximately  Approximately 

Nitrogen  78%  Nitrogen  78%  None 

Oxygen  21%  Oxygen  16%  Loss  25% 

Carbon  dioxide  .03%  Carbon  dioxide  Increased  over  100 

4.38%  times 

Dust,  variable  Dust,  almost  none     Decreased 

Water  vapor,  variable  More  Greatly  increased 

Temperature,  variable  About  98 °F.  Increased  usually 

Iii  addition  to  the  above  changes,  there  are  added  to 
the  air  while  in  the  body  small  quantities  of  ill-smelling, 
poisonous,  organic  matter.  It  is  the  latter  which  gives 
the  bad  odor  to  a  poorly  ventilated  room. 

Necessity  of  ventilation.  We  know  that  it  is  neces- 
sary to  have  the  air  in  a  room  changed.  If  this  is  not 
done  the  room  becomes  "  close. "  We  soon  become  very 
restless,  feel  sleepy  and  stupid,  and  frequently  headaches 
result.  Experiments  seem  to  indicate  that  these  results 
are  not  brought  about  by  a  lack  of  oxygen  or  by  an  over 
abundance  of  carbon  dioxide.  They  seem  rather  to  be 
the  result  of  the  presence  of  the  organic  matter  before 
referred  to.  Much  discomfort  also  results  from  air 
which  is  too  hot  and  too  dry. 

Methods  of  ventilation.  In  order  to  ventilate  it  is 
necessary  not  only  to  remove  foul  air,  but  also  to  bring 
in  fresh  air.  According  to  some  authorities,  a  room 
is  not  well  ventilated  unless  it  supplies  each  person 
with  about  eighteen  hundred  cubic  feet  of  air  an  hour. 

In  dwelling  houses  the  amount  of  space  for  each  per- 


RESPIRATORY  SYSTEM  353 

son  is  large,  and  a  good  deal  of  air  enters  through  the 
cracks  around  the  windows  and  the  doors.  But  even 
so,  out-of-door  air  is  far  superior  to  the  air  in  houses. 
Unfortunately  in  most  dwellings  little  provision  has 
been  made  for  proper  ventilation.  Most  of  us  depend 
entirely  upon  open  windows.  If  one  window  is  opened 
at  the  bottom  to  let  fresh  air  in,  and  another  at  the 
top  to  admit  of  the  escape  of  the  warm  foul  air,  this 
method  works  pretty  well.  It  does,  however,  often 
produce  drafts,  and  as  a  rule  cools  the  air  too  much. 
Fresh  air  does  not  necessarily  mean  cold  air. 

In  tenement  buildings,  public  halls,  and  work  shops 
much  more  attention  should  be  given  to  ventilation. 
Certainly  each  of  us  has  had  the  experience  of  being 
made  very  uncomfortable  because  of  poor  air.  Air 
itself  will  not  circulate  very  rapidly.  Consequently 
in  large  buildings  it  is  necessary  to  have  it  forced  into 
the  rooms  by  large  fans  in  the  basements.  It  is  best 
to  have  fresh  air  brought  in  from  the  out-of-doors,  have 
it  Avashed  to  remove  the  dust,  then  heated,  moisture 
added,  and  fanned  around  to  the  rooms.  It  is  well  to 
have  this  warm  air  enter  at  the  top  of  the  room. 
Then  as  it  cools  and  becomes  foul  it  settles  to  the  lower 
part  of  the  room  from  which  it  should  be  removed. 

Diseases  of  the  respiratory  organs.  There  are  many 
diseases  which  attack  one  or  more  parts  of  the  organs 
used  in  breathing.  Many  of  these  are  the  so-called 
"impure"  air  diseases,  while  others  have  a  different 
origin. 


354  A  YEAR  IN  SCIENCE 

Adenoids.  This  is  the  name  given  to  certain  growths 
which  appear  in  the  upper  part  of  the  throat  just 
behind  the  nasal  opening.  They  often  occur  in  grow- 
ing children.  Sometimes  they  become  so  large  that 
they  close  the  nasal  openings,  and  hence  make  mouth 
breathing  necessary.  By  closing  the  Eustachian  tubes 
they  may  be  the  cause  of  deafness.  Adenoids  in  them- 
selves are  not  dangerous.  They  may  shrink  and  dis- 
appear. However,  they  are  often  the  indirect  cause 
of  much  harm  and  should  then  be  removed. 

Tonsils.  In  the  throat  are  the  tonsils,  which  we 
know  often  cause  much  annoyance.  If  they  become 
repeatedly  inflamed,  they  should  be  removed. 

Pleurisy.  In  pleurisy  the  pleural  membranes  become 
inflamed  and  oftentimes  secrete  an  abnormal  amount  of 
fluid.  This  fluid  takes  up  space  which  the  lungs  should 
occupy. 

Contagious  diseases.  The  so-called  impure  air  dis- 
eases are  all  contagious.  Since  air  is  the  medium 
through  which  the  germs  are  carried,  it  is  evident  that 
these  diseases  are  very  readily  spread.  The  most 
common  of  these  diseases  are  colds,  tonsilitis,  diph- 
theria, bronchitis,  pneumonia,  and  tuberculosis.  With 
most  of  these  we  are  already  so  familiar  that  they 
need  little  explanation.  If  we  all  become  impressed 
with  the  fact  that  they  are  contagious  diseases  and 
put  forth  every  effort  to  prevent  their  spread,  we  have 
gone  a  long  way  toward  eradicating  them.  We  know 
what  causes  them  and  we  know  how  to  prevent  their 


RESPIRATORY  SYSTEM  355 

carriage.    They  are  all  preventable  diseases.     The  duty 
of  preventing  their  spread  rests  with  each  one  of  us. 

Vaccination  for  smallpox  was  discovered  by  Jenner 
in  1796.  Since  that  time  the  public  has  gradually 
become  convinced  of  the  advantages  of  this,  as  well  as 
other  methods  of  protection  against  that  one-time  ter- 
rible disease.  In  the  following  table  notice  the  effect 
this  has  had  upon  the  prevalence  of  the  disease.  Com- 
pare with  this  the  death  rate  due  to  impure  air  dis- 
eases and  it  will  be  evident  that  we  are  facing  a  great 
problem,  but  one  which  each  of  us  can  share  in  solving. 

CHICAGO'S  MORTALITY  FOR  THE  YEAR  1910* 

CAUSE  NUMBER  OF  DEATHS 

Smallpox 1 

Influenza .     146 

Bronchitis    171 

Tuberculosis  of  Lungs   3,366 

Pneumonia 3,526 

Questions 

1.  Why  do  all  living  things  need  air  ? 

2.  What  is  meant  by  internal  respiration?     By 
external  respiration  ? 

3.  Name  the  parts  of  the  respiratory  tract  begin- 
ning with  the  nasal  passages.     Briefly  describe   the 
structure  of  each. 

4.  Why  should  we  avoid  mouth  breathing  ? 

5.  What  are  the  chief  features  of  the  larynx? 

6.  How  is  sound  produced? 

7.  What  is  the  pleura?    What  are  its  functions? 

8.  Explain  how  the  thorax  is  enlarged. 

•From  Report  of  the  Department  of  Health  of  the  City  of 
Chicago  for  the  years  1907-1910. 


356  A  YEAR  IN  SCIENCE 

9.     What  causes  the  air  to  rush  into  the  lungs? 

10.  How  is  the  thorax  decreased  in  size?     What 
effect  does  this  have  on  the  amount  of  air  in  the 
lungs? 

11.  State  some  facts  concerning  the  capacity  of  the 
lungs. 

12.  Of  what  use  are  the- air  sacs? 

13.  What  changes  take  place  in  the  air  while  it  is 
in  the  lungs? 

14.  How  can  you  account  for  these  changes'? 

15.  Describe  foul  air  and  its  effect  on  health. 

16.  Explain  fully  how  to  Tentilate  a  room. 

17.  How  much  pure  air  is  required  for  each  person 
per  hour? 

18.  Why  should  the  air  in  a  room  be  kept  moist? 

19.  What  are  adenoids?     How  may  they  interfere 
with  the  health? 

20.  Locate  the  tonsils. 

21.  Name  five  so-called  impure  air  diseases. 

22.  Are  they  preventable  diseases? 

23.  Why  should  colds  not  be  neglected? 

24.  What  was  the  death  rate  from  tuberculosis  in 
Chicago*  in  1910? 

25.  How  does  this   compare  with  the  number   of 
deaths  from  smallpox? 

26.  How  can  you  account  for  this  difference? 

27.  Why  is  tuberculosis  called  the  white  plague? 

28.  How    may   tuberculosis    be   spread?     Suggest 
methods  for  preventing  its  spread. 

29.  Is  tuberculosis  hereditary? 

30.  What  can  you  personally  do  to  guard  against 
contracting  tuberculosis? 

31.  What    can    you.   do    to    help    to    decrease    the 
amount  of  tuberculosis? 


CHAPTER  XLIII 
EXCRETORY  SYSTEM 

General.  A  furnace  must  not  only  be  supplied  with 
fuel  and  air,  but  from  it  must  constantly  be  removed 
smoke  and  ashes.  Every  boy,  at  least,  appreciates  the 
amount  of  ashes  formed  and  the  importance  of  their 
removal. 

We  already  know  how  our  bodies  are  supplied  with 
food  and  oxygen.  We  also  know  that  in  the  process  of 
living,  parts  of  the  body  are  constantly  being  oxidized 
and  other  parts  are  being  worn  out.  As  a  result  of 
these  destructive  processes,  tcaste  products  are  formed. 
Chief  among  these  are  carbon  dioxide,  water,  and  urea. 

The  organs  used  in-  the  elimination  of  these  Avastes 
are  the  lungs,  the  skin,  the  kidneys,  and  to  some  extent, 
the  liver.  These  are  known  as  excretory  organs.  Which 
of  the  waste  products  are  removed  by  the  lungs? 

The  kidneys.  The  kidneys  are  organs  through  which 
urea  (nitrogenous  waste)  and  water  are  removed  from 
the  blood.  In  addition  to  these  the  kidneys  excrete 
some  carbon  dioxide,  salts,  and  small  quantities  of  other 
substances.  On  each  side  of  the  backbone  in  the 
abdominal  cavity  lie  two  bodies  about  five  inches  long. 
These  are  the  kidneys.  In  the  figure  notice  the  shape 

357 


358 


A  YEAR  IN  SCIENCE 


—  Vein 


and  the  .exact  location  of  them.     From  each  of  the 
kidneys  a  tube,  the  ureter,  passes  to  the  bladder.     The 

latter  is  a  muscular 
sac  situated  in  the 
lower  part  of  the  ab- 
dominal cavity.  From 
y  it  a  tube,  the  urethra, 
carries  the  urine  to 
the  external  urinary 
opening. 

Each  kidney  is  com- 
posed of  an  enormous 
number  of  compli- 
cated tubes.  Around 
these  tubes  are  many 
blood  capillaries. 
From  the  blood,  while 
it  is  in  the  kidneys, 
there  is  removed,  by 
means  of  secreting 
cells  in  the  tubes, 
large  quantities  of  water  holding  in  solution  urea 
and  the  other  excretions  from  the  kidneys.  This 
waste  material  is  called  urine.  From  these  tubes 
the  urine  passes  into  a  cavity  in  the  kidney  from  which 
it  is  poured  through  the  ureter  to  the  bladder.  When 
a  sufficient  amount  has  collected  in  the  bladder,  the 
muscular  walls  contract  and  it  is  expelled.  It  will  thus 
be  seen  that  the  kidneys  do  not  make  the  waste 


Bladde 


UrethYa 


Fig.    167.      The  kidneys   and   their 
connections. 


EXCRETORY  SYSTEM 


359 


Corte 


Pelvis 


products  which  they  excrete,  but  only  remove  them 
from  the  blood. 

Sometimes  extra  waste  products  are  sent  to  the  kid- 
neys for  removal. 
They  become  over- 
w  or  k  e  d  ,  poisonous 
substances  collect, 
and  severe  illness  en- 
sues. Unless  the  de- 
fect is  remedied  death 
may  result,  for  the 
work  of  the  kidneys 
is  indispensable  to 
the  body. 

Theskin.  The 
whole  outer  surface 
of  our  bodies  is  cov- 
ered with  a  flexible,  elastic  tissue,  the  skin.  This 
varies  in  thickness  and  in  texture.  On  the  palm  of 
the  hand  and  the  sole  of  the  foot  it  is  thick  and 
tough ;  the  covering  of  the  lips  is  extremely  thin.  The 
hair  and  nails  are  modifications  of  it. 

Ordinarily  we  do  not  appreciate  the  great  importance 
of  the  skin.  It  has  at  least  four  important  uses.  First, 
its  most  obvious  use  is  that  of  protection  for  the  muscles 
and  other  organs  which  lie  beneath  it.  It  keeps  them 
from  drying;  prevents  the  irritation  which  would 
result  from  contact  with  clothing;  and  also  keeps 
bacteria  from  entering  the  body.  Second,  it  contains 


Medulla 


Fig.    168.     Longitudinal  section   of  a 
kidney. 


360  A  YEAR  IN  SCIENCE 

a  countless  number  of  organs  at  the  ends  of  nerves  by 
means  of  which,  we  receive  messages  of  temperature 
and  touch.  Third,  by  means  of  perspiration  it  throws 
off  a  great  deal  of  water  and  small  quantities  of  other 
waste  materials.  Fourth,  it  is  the  chief  means  of 
regulating  the  temperature  of  the  body. 

Structure.  As  we  might  infer  from  all  of  these  uses, 
the  skin  is  a  complex  organ.  It  consists  of  two  layers; 
the  outer  is  called  the  epidermis,  and  the  inner  the 
dermis. 

The  epidermis  is  formed  of  layers  of  cells.  It  con- 
tains no  blood  vessels  and  hence  it  is  possible  to  prick 
this  layer  without  causing  bleeding.  The  growing  cells 
are  at  the  bottom  of  the  epidermis,  where  they  absorb 
nourishment  from  the  dermis  beneath.  As  these  cells 
grow  and  increase  in  numbers  they  crowd  the  cells 
above  away  from  the  source  of  supply  and  they  become 
thinner  and  drier  until  they  become  hard  scales.  These 
scales  are  constantly  being  worn  and  washed  away. 
Scattered  among  the  lower  cells  of  the  epidermis  are 
some  cells  which  contain  pigment,  or  coloring  matter. 
An  abundance  of  these  cells  gives  the  black  color  to 
the  skin  of  the  negro. 

The  dermis  is  composed  mainly  of  a  loose  network 
of  fibrous  tissue.  In  this  are  embedded  numerous  blood 
vessels,  nerves,  sweat  and  oil  glands,  and  the  roots  of 
the  hair.  In  the  deeper  parts  of  the  dermis  are  groups 
of  fat  cells.  These  fill  up  the  inequalities  left  by  the 
tissues  below  the  skin  and  make  it  smooth  and  plump. 


EXCRETORY  SYSTEM  361 

Sweat  glands.  If  the  outer  surface  of  the  skin  is 
examined  with  a  hand  lens,  many  minute  pores,  or 
openings,  will  be  seen.  These  are  the  openings  of  the 
sweat  glands  which  lie  embedded  in  the  lower  part  of 
the  dermis.  Around  each  sweat  gland  is  a  network  of 
blood  vessels.  As  the  blood  flows  through  these  capil- 
laries, the  glands  take  from  it  a  fluid  from  which  they 
produce  sweat  or  perspiration.  This  is  over  99%  water, 
dissolved  in  which  are  some  salts  and  nitrogenous  waste. 
Perspiration  is  an  excretion,  but  its  chief  function,  as 
we  shall  see  later,  is  to  regulate  the  temperature  of  the 
body. 

The  hair.  The  hair  is  an  outgrowth  from  the  epi- 
dermis. Each  hair  is  situated  in  a  tube-like  sac  called 
the  follicle,  formed  by  the  epidermis  dipping  down  into 
the  dermis.  At  the  bottom  of  the  follicle  is  a  little 
bulb  made  of  capillaries  and  nerves.  It  is  from  this 
bulb  that  the  hair  grows  in  length,  and  from  this  a 
new  hair  grows  to  replace  an  old  one.  A  hair  is  a 
slender  tube  of  hard  dry  cells,  the  interior  of  which  is 
filled  with  cells  containing  coloring  matter.  Opening 
into  the  hair  follicle  are  the  ducts  from  the  oil  glands. 
The  secretion  from  these  glands  keeps  the  skin  moist 
and  also  makes  the  hair  soft  and  more  pliable.  The 
glands  may  be  made  more  active  by  massaging  and 
vigorous  brushing.  If  the  hair  is  kept  properly  oiled, 
it  does  not  become  so  brittle,  and  consequently  is  less 
liable  to  break  or  to  split. 

The  condition  of  the  hair  depends  upon  the  healthful- 


362 


A  YEAR  INT  SCIENCE 


ness  of  the  scalp.  The  falling  out  of  hair  is  usually 
due  to  a  lack  of  nourishment  at  its  root.  If  the  bulbs 
of  the  hair  are  dead,  no  substance  will  make  it  grow. 


Fat  Cells 
Fig.   169.     A  section  of  the  skin  highly  magnified. 

Therefore,  no  attention  should  be  paid  to  the  adver- 
tisements of  hair  tonics  claiming  that  they  will  make 
hair  grow  on  bald  heads.  Hair  may  be  invigorated  by 
massaging  the  scalp  daily,  but  .aside  from  that,  its 
growth  cannot  be  increased  by  any  home  remedies. 

Fright,  anxiety,  or  great  care  may  turn  the  hair 
gray  in  a  very  short  time,  but  usually  the  color  dis- 


EXCRETORY  SYSTEM  363 

appears  gradually  after  the  age  of  forty.  Little  by 
little  the  system  fails  to  supply  the  coloring  matter  for 
the  central  part  of  the  hair.  Its  place  is  taken  by  air. 
There  is  no  way  of  preventing  this  change. 

The  nails.  The  nails  are  hardened  epidermis. 
They  grow  from  the  root  which  is  underneath  the  skin 
and  are  gradually  pushed  forward.  Their  function 
is  to  protect  the  ends  of  the  fingers  and  toes.  They 
should  be  kept  trimmed  even  with  the  tip  of  the  finger. 
The  skin  at  the  base  of  the  nail  should  be  rubbed  back 
to  keep  it  from  adhering  to  the  nail. 

Temperature  of  the  body.  Our  bodies  are  usually 
warmer  than  the  things  around  us,  but  the  interesting 
fact  is  that  our  temperature  is  always  the  same,  about 
98.5°  F.  The  body  is  thus  as  warm  on  a  cold  day  as 
it  is  on  a  hot  day.  If  the  temperature  of  the  body  does 
not  change,  the  amount  of  heat  produced  must  be 
equal  to  the  amount  of  heat  lost.  If  a  greater  amount 
of  heat  is  produced,  a  greater  amount  must  be  lost 
and  vice  versa.  We  will  now  consider  how  heat  is 
produced  in  the  body,  and  how  it  is  lost. 

Source  of  heat.  The  source  of  heat  in  the  body  is  the 
result  of  the  process  of  slow  oxidation,  wrhich  is  con- 
stantly taking  place.  Since  the  muscles  form  so  large 
a  portion  of  the  body  they  contribute  the  most  of  the  heat. 
The  heat  produced  in  different  parts  of  the  body  is 
distributed  by  the  blood.  In  passing  through  an  organ 
producing  heat  the  blood  becomes  warmer,  and  then  as 
it  circulates  through  different  parts  of  the  body,  this 


364  A  YEAR  IX  SCIEXCK 

heat  is  given  up  to  the  cooler  parts.  Heat  also  travels 
by  conduction  from  the  warmer  to  the  colder  parts. 

Cooling'  the  body.  Usually  too  much  heat  is  pro- 
duced. The  body  is  then  brought  to  the  proper  tem- 
perature by  cooling,  a  process  which  is  brought  about 
through  the  skin.  If  the  body  is  too  warm,  the  blood 
vessels  in  the  skin  enlarge  and  the  blood  supply  to  the 
skin  is  greatly  increased.  As  a  result  the  skin  becomes 
very  warm.  It  is  then  cooled  by  radiation,  conduction, 
and  by  the  evaporation  of  perspiration. 

We  can  easily  feel  the  heat  given  off  by  the  skin 
through  radiation  and  conduction.  If  too  much  heat 
is  being  lost  in  this  way,  the  blood  vessels  in  the  skin 
contract  and  less  blood  flows  through  it.  Perspiration 
is  being  produced  nearly  all  the  time.  If  the  body  is 
not  warm,  the  amount  of  perspiration  is  small  and 
dries  up  as  soon  as  it  is  produced. ,  If,  however,  the 
body  becomes  very  warm  because  of  increased  activity 
in  work  or  play,  or  if  the  surrounding  temperature  is 
very  high,  more  perspiration  is  produced.  The  body 
becomes  covered  with  a  layer  of  water.  In  order  to 
evaporate  this,  heat  is  taken  from  the  skin ;  in  this  way, 
the  temperature  is  lowered. 

By  radiation  and  conduction  it  would  be  impossible 

to  cool  the  body  if  the  temperature  of  the  atmosphere 

» 

was  over  98.5°  F.  By  the  evaporation  of  perspiration, 
however,  the  temperature  can  be  lowered  even  in  the 
torrid  regions. 

All  of  this  fine  adjustment  between  the  amount  of 


EXCRETORY  SYSTEM  355 

heat  produced  and  the  amount  lost  is  brought  about 
and  regulated  through  the  action  of  the  nervous 
system. 

Clothing.  In  cold  climates  clothing  helps  to  keep 
the  body  warm  by  checking  radiation  and  by  keeping 
off  currents  of  air  which  would  carry  heat  away.  For 
this  purpose  our  clothing  should  be  made  of  materials 
which  are  poor  conductors  of  heat,  such  as  silk  and 
wool.  Linen  and  cotton,  on  the  other  hand,  are  good 
conductors  of  heat.  Under  what  conditions  should  they 
be  worn? 

Care  of  skin.  The  various  excretions  from  the  skin 
are  constantly  collecting  on  its  surface.  These  together 
with  the  dirt  from  the  air  around  us  must  be  removed, 
otherwise  they  would  soon  clog  the  ducts  from  the 
pores  and  so  interfere  with  the  work  of  the  skin. 

Warm  baths  are. necessary  for  cleansing.  To  aid  in 
removing  the  oily  secretions  from  the  skin  a  good  soap 
should  be  used.  In  addition  to  cleansing,  the  warm 
bath  opens  the  pores,  causes  the  blood  vessels  in  the 
skin  to  dilate,  and  this  increases  the  amount  of  per- 
spiration. Warm  baths  should  be  taken  before  going 
to  bed. 

Cold  baths  should  be  taken  as  a  stimulus.  The  best 
time  for  such  a  bath  is  immediately  on  rising  in  the 
morning.  It  should  last  "but  a  few  minutes  and  should 
be  followed  by  vigorous  rubbing.  The  cold  bath  is 
not  advisable  for  all  persons ;  for  some  it  is  beneficial, 
for  others  it  is  too  severe  and  should  not  be  taken. 


366  A  YEAK  IN  SCIENCE 

Paints,  powders,  and  other  external  applications  for 
beautifying  the  complexion  not  only  do  not  beautify 
it  but  are  often  injurious.  They  always  clog  the  pores 
and  sometimes  they  contain  poisonous  substances.  Any- 
thing which  will  tend  to  improve  the  health  of  the  body 
such  as  good  exercise,  plenty  of  fresh  air,  and  the 
proper  food  will  improve  the  skin  and  make  it  far 
more  beautiful  than  any  artificial  applications. 


Questions 

1.  Name  the  principal  waste  products  in  the  body. 

2.  By  means  of  what  organ  is  each  removed  from 
the  body? 

3.  Why  is  it  important  that  these  waste  materials 
should  be  removed? 

4.  Where  are  the  kidneys  located  in  the  body? 

5.  Describe  the  structure  of  the  kidneys. 

6.  How  do  the  kidneys  work? 

7.  Name  four  functions  of  the  skin. 

8.  What  is  the  structure  of  the  epidermis? 

9.  Name  the  parts  found  in  the  dermis. 

10.  Describe   the    sweat    glands.      State    definitely 
their  functions. 

11.  What  is  the  best  treatment  for  keeping  the  hair 
in  a  good  condition? 

12.  Explain  fully  the  source  of  heat  in  the  body, 
how  this  heat  is  distributed,  and  how  the  temperature 
of  the  body  is  regulated. 

13.  How  may  the  complexion  be  improved? 

14.  What  are  the  best  methods  for  taking  care  of 
the  skin? 


CHAPTER  XLIV 

DUCTLESS  GLANDS 

Introduction.  In  different  parts  of  the  body  there 
are  a  number  of  organs  which  do  not  seem  to  belong 
to  any  of  the  general  systems.  These  organs  are  glands. 
AVe  have  already  learned  that  the  cells  of  the  glands 
take  from  the  blood  fluids,  some  of  which  they  change 
chemically  and  then  excrete  them  into  another  cavity. 
For  instance,  the  salivary  glands  make  saliva  from  the 
fluid  which  they  take  from  the  blood.  This  saliva  is  then 
poured  into  a  small  tube,  or  duct,  from  which  it  is 
emptied  into  the  mouth. 

There  are,  however,  some  glands  which  do  not  empty 
their  secretions  into  any  duct  or  cavity.  Whatever 
substances  they  form  are  poured  directly  into  the 
blood.  Such  glands  are  known  as  the  ductless  glands, 
and  their  secretions  are  called  internal  secretions.  It 
is  very  difficult  to  determine  the  functions  of  these 
glands.  "We  still  know  very  little  about  many  of  them. 

Lymph  glands.  Scattered  along  the  course  of  the 
lymph  vessels  there  are  small  rounded  masses  of  tissue 
called  lymph  glands.  These  are  especially  numerous 
around  the  hip  and  shoulder  joints;  their  function 

367 


368  A  YEAR  IN  SCIENCE 

is  not  fully  known.  Some  white  corpuscles  are  pro- 
duced in  them.  To  some  extent  they  also  act  as  filters, 
for  the  lymph,  after  passing  through  them,  has  had 
most  of  the  bacteria  removed  from  it.  These  are  prob- 
ably destroyed  in  the  lymph  glands. 

Adrenal  bodies.  Just  in  front  of  each  kidney  there 
is  a  small  gland,  called  the  adrenal  body.  The  substance 
which  it  secretes  influences  the  muscles  in  the  walls 
of  the  arteries.  As  a  result  they  contract  and  reduce 
the  size  of  the  artery.  The  secretion  from  these  bodies 
helps  to  regulate  the  size  of  the  blood  vessels  and 
consequently  to  regulate  the  blood  pressure.  An  extract, 
adrenalin,  is  made  from  the  adrenal  bodies  of  sheep. 
This  is  used  to  check  hemorrhages. 

Thyroid  glands.  The  thyroid  glands  are  located  on 
the  ventral  side  (front)  of  the  neck  just  a  little  below 
the  larynx.  The  secretion  from  these  glands  seems 
necessary  for  the  proper  nourishment  and  development 
of  the  body.  Without  them  both  the  body  and  mind 
are  not  fully  developed,  a  condition  known  as  cretin- 
ism. Sometimes  the  glands  become  enlarged  and  pro- 
duce a  goiter.  In  that  case  they  produce  too  much 
secretion  and  the  activities  of  the  cells  become  greatly 
increased.  A  very  rapid  pulse,  headaches,  and  some- 
times insanity  may  result.  Goiters  should  not  be 
neglected.  As  soon  as  any  enlargement  of  these  glands 
appears  a  physician  should  be  consulted. 

An  extract  is  made  from  the  thyroid  glands  of 
sheep,  which  is  used  in  cases  wrhere  the  thyroid  glands 


DUCTLESS  GLANDS  369 

are  lacking  or  where  they  do  not  produce  enough 
secretion. 

The  spleen.  At  the  left  of  the  stomach  is  a  reddish 
brown  organ,  the  spleen,  held  in  position  by  folds  of 
the  mesentery.  It  is  of  considerable  importance,  but 
its  exact  functions  are  not  known.  Like  the  lymph 
glands,  it  produces  white  blood  corpuscles.  Some 
authorities  think  that  it  is  also  used  to  disintegrate  the 
dead  red  blood  corpuscles. 

The  pancreas.  Not  only  does  the  pancreas  furnish 
digestive  juices,  but  it  also  produces  other  important 
substances  which  enter  the  blood.  These  substances 
seem  to  regulate  the  amount  of  sugar  which  is  present 
in  the  blood.  If  the  blood  contains  too  much  sugar,  it 
is  carried  to  the  kidneys  and  results  in  the  disease 
known  as  diabetes.  In  many  cases,  this  is  supposed  to 
result  from  the  failure  of  the  pancreas  to  do  its  work 
properly. 

Questions 

1.  What  is  meant  by  internal  secretions? 

2.  Name  the  chief  ductless  glands. 

3.  Discuss  the  function  of  each  of  these  glands. 

4.  What   is  the   cause   of   goiter?     Explain   why 
goiters  should  not  be  neglected. 

5.  Define  cretinism. 


CHAPTER  XLV 

SKELETAL  SYSTEM. 

General.  You  are  all  familiar  with  animals  which 
have  no  hard  matter  in  their  bodies  at  all,  such  as  the 
jelly-fishes  and  worms.  Other  animals  such  as  insects, 
crayfishes,  and  clams,  have  a  hard  outer  covering.  This 
outside  skeleton  is  preferable  to  none  because  it  gives 
the  animal  some  rigidity  and  some  protection.  It  is 
very  inconvenient,  however,  for  in  most  cases  it  does 
not  permit  of  any  growth.  As  a  result  it  must  fre- 
quently be  shed,  and  then  for  a  short  period  the  animal 
is  left  with  only  a  soft  outer  covering. 

In  the  higher  animals  there  is  a  well  developed  inner 
framework  of  bones.  In  the  human  body  this  skeleton 
is  composed  of  over  two  hundred  separate  bones.  These 
are  joined  and  serve  several  purposes:  1.  They  give 
shape  and  rigidity  to  the  body.  2.  They  protect  the 
delicate  organs  of  the  body.  3.  They  provide  places  for 
the  attachment  of  muscles,  and  serve  as  levers  upon 
which  the  muscles  may  act. 

Regions  of  the  skeleton.  For  convenience  the  bones 
of  the  skeleton  may  be  divided  into  three  groups, 
namely : 

370 


SKELETAL  SYSTEM 


371 


1.  The  bones  of  the  head. 

2.  The  bones  of  the  neck    and 
trunk. 

3.  The  bones  of  the  arms  and 
of  the  legs  together  with  those  of 
the  shoulders  and  the  hips. 

The  head.  The  bones  of  the 
skull,  except  that  of  the  lower 
jaw,  are  united  firmly  together. 
They  are  divided  into  two  regions, 
the  cranium,  or  brain  case,  and 
the  face.  The  bones  of  the  cran- 
ium are  large  and  flat,  while  those 
of  the  face  are  irregular  in  shape. 

The  trunk.  The  trunk  consists 
of  the  following  parts: 

1.  A  main  axis,  the  spinal  or 
vertebral  column.     . 

2.  The  ribs. 

3.  The  breast  bone. 

The  vertebral  column  consists  of 
a  number  of  separate  bones,  called 
vertebrae,  placed  one  upon  another. 
It  is  divided  into  regions  as 
follows : 

1.  The  cervical,  or  neck  region,  consisting  of  seven 
vertebrae. 

2.  The  dorsal  region,  or  region  of  the  back,  consist- 
ing of  twelve  vertebrae  to  which  the  ribs  are  attached. 


Fig.  170.    Side  view 
of  spinal  column. 


372  A  YEAR  IN  SCIENCE 

3.  The  lumbar  region,  or  region  of  the  loins,  con- 
sisting of  five  vertebrae. 

4.  The   sacral   region,    consisting   of    five    vertebrae 
united  to  form  a  single  bone,  the  sacrum. 

5.  The  coccygeal  region,  four  small  vertebrae  united 
to  form  one  bone,  the  coccyx. 

In  the  diagram  locate  these  regions.  To  which  verte- 
brae are  the  ribs  attached?  Compare  the  vertebrae 
in  size.  "What  advantage  is  this  difference  in  size  ? 

Passing  through  the  vertebral  column  is  a  canal 
through  which  the  spinal  cord  extends  and  connects 
with  the  brain  at  the  base  of  the  skull. 

Ribs  and  sternum.  There  are  twelve  pairs  of  slen- 
der curved  bones  called  the  ribs.  We  have  already 
observed  their  attachment  at  the  back.  The  first  seven 
pairs  are  joined  at  the  front  by  means  of  cartilage  to 
the  breast  bone,  or  sternum;  the  eighth,  ninth,  and  tenth 
pairs  are  attached  to  the  cartilage  of  the  seventh 
pair;  the  last  two  pairs  are  free  or  floating  ribs. 

Bones  of  limbs.  The  upper  limbs,  or  arms,  are 
attached  to  the  shoulder  blades  and  collar  bones.  The 
lower  limbs,  or  legs,  are  attached  to  the  hip  bones.  The 
hip  bones  are  large  and  firmly  united  to  the  sacrum.  Of 
what  advantage  is  this? 

The  bones  of  the  arms  and  those  of  the  legs  are 
arranged  on  the  same  plan.  Locate  the  following  bones 
in  Figure  171. 

Arm — humerus  Wrist — 8  carpals 

Forearm — radius  and  ulna     Hand — 5  metacarpals 


SKELETAL  SYSTEM 


373 


Kneecap — patella 
Ankle — 7  tarsals 
Foot — 5  metatarsals 

each  toe,  except  the  big 

toe,  which  has  two 

Scapula 


Pelvis 


Hum  ems 


Peimu 


Fingers — 14  phalanges,   3 

in  each  finger  and  2  in 

the  thumb 

Leg — tibia  and  fibula 
Thigh — femur 

Composition 
of  bone.  If  we  place 
a  rib  in  a  bottle  of 
dilute  hydrochloric 
acid  and  let  it  stand 
a  few  days,  we  shall 
find  that  it  has 
changed.  The  shape 
remains  the  same,  but 
the  bone  becomes  soft 
and  elastic.  It  can 
easily  be  cut  with  a 
knife,  and  it  will  be 
found  to  be  so  flexible 
that  it  can  be  tied  in 
a  knot.  The  sub- 
stance of  which  it  is 
now  composed  is  ani- 
mal matter,  or  carti- 
lage. 

By  burning  a  bone 
in  a  fire  this  animal  matter  can  be  removed.  Again  the 
form  of  the  bone  does  not  change.  After  this  process, 
however,  the  bone  is  left  white  and  brittle.  The  sub- 


Paiella— ( 


adiirs 


ajpajs 


hafanges 


Fig.    171. 


-Tarsals 
Metatarsais 
Phalanges 


Bones   of   the   leg   and   the 
arm. 


374  A  YEAR  IX  SCIENCE 

stance  now  left  is  mineral  matter,  chiefly  calcium  car- 
bonate and  calcium  phosphate. 

In  an  adult  about  two-thirds  of  the  bone  is  mineral 
matter.  In  a  child  there  is  much  less.  As  a  result,  the 
bones  of  a  child  are  much  more  flexible  than  those  of 
an  adult. 

Growth  of  bone.  Bone  is  not  a  solid  compact  mass, 
as  one  might  be  led  to  suppose  from  its  appearance. 


Canal 

Canal 


Fig-.   172.     Sections  through  bone  highly  magnified  ;  A,  longitudinal 
section ;   B,  cross  section. 


If  a  section  of  a  bone  is  examined  with  a  microscope, 
it  will  be  found  to  be  composed  of  a  series  of  canals 
and  irregular  cavities.  These  canals  contain  blood 
which  passes  through  smaller  canals  to  the  bone  cells 
which  lie  in  the  irregular  cavities.  These  bone  cells 
absorb  the  food  and  transform  it  into  bone  material. 

Covering  the  bone  everywhere  except  at  the  joints 
is  a  tough  membrane  called  the  periosteum.  This  mem- 
brane is  of  great  importance  in  the  growth  of  the  bone, 
because  the  new  bone  is  formed  by  the  cells  of  the 
periosteum.  If  a  bone  is  broken,  or  if  a  piece  is  taken 


SKELETAL  SYSTEM 


375 


~  Ij"  _  Periosteum 


Spongy  Bone 


:£•  -  Marrow  Cavity 


-Hard  .Bone 


Fig.  173.    A  long  bone  cut 
lengthwise. 


firmly  fastened  to- 
gether that  little  or 
no  movement  is  pos- 
sible. In  other  cases, 
they  move  easily,  one 
on  the  other. 


out,  the  periosteum  adds  new 
cells  which  become  bone  tissue 
and  repair  the  injury. 

Joints.  Where  two  bones  come 
together  they  form  a  joint. 
Sometimes  the  bones  are  so 


Pefvis 


Fig.  174.     The  hip  joint 


In  joints,  like  the  hip,  the  bones  are  held  together 
by  bands  of  tough  material  called  ligaments.  They  are 
further  held  together  by  a  covering  of  connective  tissue 
and  by  the  muscles. 

Hygiene  of  the  skeleton.  Since  the  bones  of  children 
are  soft  and  flexible,  it  is  very  easy  for  them  to 
become  distorted.  Bowlegs,  for  example,  are  often  the 
result  of  allowing  children  to  walk  too  soon.  The  bones 


376 


A  YEAR  IN  SCIENCE 


have  not  become  sufficiently  stiffened  to  resist  the  pres- 
sure of  the  weight  of  the  body.  Round  shoulders  often 
result  from  a  careless  position  of  the  body. 

Some  germ  diseases  also  attack  the  bones,  among 
them  tuberculosis,  which  sometimes  causes  a  deformity. 
A  common  cause  of  deformity  of  the  bones  in  small 
children  is  lack  of  the  proper  kind  of  nourishment. 
Lime  salts  are  necessary  for  stiffening  the  bones,  and  a 


From  Blount,  Physiology  and  Hygiene,  Row,  Peterson  &  Co. 
Fig.    175.      Fractures;   A,   a   "green   stick"   fracture   of   the   radius; 
B,  a   fracture  of   the   tibia. 

lack  of  these  salts  in  the  food  results  in  a  disease  called 
the  rickets,  which  causes  weak  and  crooked  bones. 
In  a  fracture  the  bone  is  broken.    To  treat  a  fracture, 


SKELETAL  SYSTEM  377 

the  pieces  of  bone  must  be  brought  back  into  position 
(this  is  called  "setting"  the  bone),  and  must  be  held 
there  by  splints  until  the  ends  have  become  firmly 
knitted  together.  It  is  essential  that  the  bone  be  kept 
quiet  until  the  ends  have  "knitted." 

Sometimes  a  bone  in  moving  slips  out  of  place.  This 
is  a  dislocation.  Parts  of  the  ligaments  are  sometimes 
torn,  and  the  bone  may  or  may  not  be  dislocated.  Such 
an  accident  is  a  sprain.  This  is  often  very  painful,  slow 
to  heal,  and  should  be  treated  with  care. 

Questions 

1.  Of  what  use  are  the  bones? 

2.  What  are  the  three  parts  of  the  skeleton? 

3.  On  your  head  locate  the  two  parts  of  the  skull. 

4.  Describe  the  structure  of  the  vertebral  column. 

5.  How  many  ribs  are  there?     To  what  are  they 
attached? 

6.  Name  the  bones  in  the  upper  limb.    In  the  lower 
limb. 

7.  How  does  the  arrangement  of  the  bones  in  the 
arm  differ  from  that  in  the  leg? 

8.  Give  the  composition  of  bone. 

9.  Discuss  the  growth  of  bone. 

10.  Describe  a  joint. 

11.  Why  should  not  a  heavy  strain  be  put  upon  the 
bones  of  children? 

12.  What   is  meant  by :   rickets,   fracture,   disloca- 
tion, sprain? 


CHAPTER  XLVI 
MUSCULAR  SYSTEM 

Importance.  The  muscles  .of  our  body  constitute 
about  one-half  of  its  weight.  By  means  of  these  mus- 
cles all  the  movements  of  the  body  and  of  its  organs 
are  produced.  Not  only  do  they  bring  about  the  more 
obvious  motions  of  the  legs  and  the  arms,  but  also  to  their 
action  are  due  the  contractions  of  the  heart,  of  the 
stomach,  and  of  the  other  internal  organs. 

Structure.  In  this  study  we  will  consider  only  the 
larger  muscles  which  are  attached  to  the  skeleton. 
Muscles  are  of  various  shapes,  but  they  are  usually 
larger  in  the  middle  than  at  either  end.  They  are 
attached  at  both  ends  to  bones,  usually  by  a  tough, 
white,  inelastic  cord,  or  tendon. 

If  a  complete  muscle  is  examined,  it  will  be  found 
to  be  covered  with  a  thin  sheet  of  connective  tissue. 
Y7hen  this  is  removed,  the  muscles  can  readily  be 
divided  longitudinally  into  bundles.  These  can  be  split 
into  smaller  bundles,  which  in  turn  can  be  divided  into 
a  number  of  long  fibers.  These  fibers  have  the  power 
to  contract  and  thus  to  become  shorter  and  thicker. 
When  they  shorten,  they  pull  on  the  bone  to  which 
they  are  fastened  and  move  it.  Their  force  is  always 

378 


MUSCULAR  SYSTEM  379 

the  result  of  a  contraction,  and  hence  is  due  always 
to  a  pull  and  never  to  a  push. 

Tendons  are  useful  because  they  permit  the  thick 
contracting  part  of  the  muscle  to  be  at  some  distance 
from  the  part  to  be  moved.  This  avoids  bulkiness,  espe- 
cially at  the  joints.  The  muscles  which  move  the 
finger,  for  example,  are  located  in  the  forearm.  Ten- 
dons, which  can  easily  be  traced  on  the  back  of  the 
hand,  extend  from  these  muscles  to  the  finger  bones. 
It  is  evident  that  this  arrangement  makes  the  hand 
smaller  and  more  graceful  and  permits  of  greater 
ease  and  delicacy  in  its  movements. 

Blood  and  nerve  supply.  Muscles  are  well  supplied 
with  blood.  Fresh  meat  is  always  deep  red  in  color 
due  to  the  presence  of  a  great  quantity  of  blood. 
Nerves  are  also  very  numerous  in  muscles ;  in  fact,  some 
muscles  are  altogether  under  the  control  of  the  nervous 
system,  and  are  known  as  voluntary  muscles.  Most  of 
the  muscles  fastened  to  the  bones  are  of  this  type.  Other 
muscles,  such  as  those  in  the  walls  of  the  stomach, 
in  the  walls  of  the  blood  vessels,  or  in  the  heart  are 
perhaps  not  completely  under  nerve  control.  At  any 
rate,  we  can  not  control  them  and  they  are  called 
involuntary  muscles. 

Action  of  muscles.  The  action  of  a  muscle  can  best 
be  understood  by  a  consideration  of  the  arm  muscles. 
The  forearm  is  bent  or  flexed  by  the  action  of  a  large 
muscle  on  the  front  of  the  arm,  known  as  the  biceps 
muscle.  This  is  attached  by  two  tendons  to  the 


380  A  YEAR  IX  SCIENCE 

shoulder  blade.  The  muscle  then  passes  over  the  front 
of  the  humerus.  Just  below  the  elbow  joint  it  is 
attached  by  a  tendon  to  the  radius.  When  the  biceps 


Tendon 


Fig.  176.  The  arm  showing  the  attachments  of  the  biceps 
muscle.  If  the  muscle  contracts  slightly  the  forearm  will  be  lifted 
over  a  great  distance. 

contracts  the  distance  between  the  forearm  and  the 
shoulder  is  shortened.  As  a  result,  the  forearm  is  bent 
on  the  arm.  If  the  biceps  is  decreased  only  a  few 
inches  in  length,  the  hand  is  moved  through  a  much 
greater  distance. 

Situated  on  the  back  of  the  arm  is  the  large  triceps 
muscle.  By  its  contraction  the  forearm  is  straightened, 
or  extended.  Where  must  its  attachments  be  in  order 
to  produce  this  action? 

Results  of  muscular  action.  The  results  of  muscular 
action  are  familiar  to  all  of  us.  We  know  that  motion, 
heat,  and  energy  are  produced.  To  produce  these,  oxida- 
tion is  necessary,  as  a  result  of  which  both  nerves  and 
muscles  are  being  worn  out  and  waste  products  are 


MUSCULAR  SYSTEM  381 

being  formed.  The  chief  ones  of  these  products  are 
carbon  dioxide,  water,  and  nitrogenous  wastes. 

Frequently  we  become  fatigued.  This  is  probably 
not  because  the  muscles  and  nerves  are  being  over- 
worked, but  because  the  waste  products  are  not  being 
removed  fast  enough.  A  good  blood  circulation  is  nec- 
essary to  remove  these  wastes  and  to  carry  food  and 
oxygen  for  rebuilding  the  tissues  which  are  being  used. 

Exercise.  A  certain  amount  of  vigorous  exercise 
each  day  is  essential  to  keep  the  body  in  the  best 
physical  condition,  for,  as  everyone  knows,  if  the  mus- 
cles are  not  used  for  a  time  they  become  weak  and 
flabby.  Regularity  in  exercise  is  as  important  as  regu- 
larity in  eating.  The  kind  and  amount  of  exercise 
should  vary  with  the  individual.  It  should  be  vigorous 
enough  so  that  one  feels  fatigued  but  not  exhausted. 
The  ideal  exercise  involves  the  action  of  the  greatest 
number  of  muscles. 

Exercise  taken  in  the  spirit  of  play  is  most  bene- 
ficial, because  it  not  only  results  in  free  and  varied 
activity,  but  it  also  rests  the  mind.  As  a  result  of 
exercise  the  whole  body  is  improved,  respiration  and 
circulation  are  increased,  the  muscles  are  developed, 
and  the  mind  is  made  more  alert  and  active. 

Questions 

1.  What  part  of  the  body  by  weight  is  muscle  ? 

2.  Of  what  use  to  the  body  are  the  muscles  ? 

3.  What  special  property  is  possessed  by  muscle? 


382  A  YEAR  IK  SCIENCE 

4.  Describe  a  typical  muscle. 

5.  What  is  the  appearance  of  muscle  as  seen  on  the 
cut  end  of  a  piece  of  meat? 

6.  What  are  tendons?    What  is  their  use? 

7.  How  are  muscles  made  to  act? 

8.  Explain  fully  how  the   arm  is  flexed   and   ex- 
tended by  the  action  of  the  biceps  and  triceps  muscles. 

9.  What  is  meant  by  the  term  voluntary,  muscle? 
Involuntary  muscle? 

10.  Name  two  voluntary  muscles  and  also  two  invol- 
untary ones. 

11.  What  is  probably  the  cause  of  fatigue? 

12.  Explain   how   and   why   the   muscles   should   be 
exercised. 

13.  Why  are  games  a  beneficial  form  of  exercise1/ 


CHAPTER  XLVII 

NERVOUS  SYSTEM 

Introduction.  In  the  preceding  chapters  we  have 
learned  that  the  body  is  composed  of  many  organs, 
each  of  which  lias  its  special  function.  The  human 
body,  however,  is  not  simply  a  collection  of  working 
organs,  but  it  is  a  complete  organism  with  its  many 
parts  Avorking  together  harmoniously. 

Even  in  very  simple  operations,  the  coordinated 
action  of  many  parts  of  the  body  is  involved.  In 
moving  the  arm,  for  example,  the  muscles  contract  and 
relax  and  as  a  result,  motion  is  produced.  In  this 
process,  however,  they  have  consumed  food  and  oxygen 
and  given  off  waste  products.  This  increases  the  activ- 
ity of  the  digestive,  respiratory,  circulatory,  and 
excretory  systems.  Obviously  it  would  be  utterly 
impossible  for  all  of  these  organs  to  work  together 
for  the  common  good,  unless  there  was  some  means  of 
communicating  the  needs  of  one  organ  to  the  others. 
There  must  also  exist  some  central  system  that  con- 
trols the  action  of  each  of  the  organs  in  our  body, 
and  brings  about  cooperation  among  them. 

Xot  only  must  the  parts  of  our  body  be  correlated 
with  each  other,  but  also  they  must  be  adjusted  to  the 

383 


384 


A  YEAR  IN  SCIENCE 


outside  world.  Parts  of  our  body  must,  receive  impres- 
sions from  the  outside  world,  and  then  these  must  be 
communicated  from  them  to  other  parts.  This  adjust- 
ment and  regulation  of  the  parts  of  the  body  to  each 
other  and  to  the  outside  world  is  the  work  of  the 
nervous  system. 

Parts  of  nervous  system. 


^vcv* 


Cell 
Body 


Axon 


-Sheath 


Endings 


177.    Diagram  to  show  the 

structure   of   a   neuron. 


The  nervous  system  con- 
sists of  nerve  centers  and 
nerves.  The  nerve  centers 
are  the  brain,  the  spinal 
oor^  and  smaller  centers 
called  ganglia  scattered  in 
different  parts  of  the  body. 
From  these  nerve  centers 
nerves  arise.  These  divide 
a  great  many  times  and 
their  branches  penetrate  all 
the  organs  and  tissues  of 
the  body. 

The  nerve  cell,  The  unit 
of  structure  in  the  nervous 
system  is  the  nerve  cell,  or 
neuron.  This  is  not  so 
simple  in  structure  as  many 
of  the  other  cells  in  the 
body.  It  consists  of  a  large 
cell  from  which  there  are 
many  projections  called 
dendrites.  One  of  these 


XKKVors  SYSTEM  385 

projections  is  greatly  elongated  and  forms  a  nerve  fiber 
which  may  be  only  a  fraction  of  an  inch  in  length  or  it 
may  be  two  or  three  feet.  Near  the  end,  a  fiber  may 
branch  abundantly,  sometimes  having  very  complex 
endings  as  in  the  eye  or  in  the  ear.  Along  its  course 
the  fiber  is  protected  by  two  coverings.  Xerve  cells 
are  found  only  in  nerve  centers. 

Nerves.  Bundles  of  nerve  fibers,  together  with  blood 
vessels  and  connective  tissue,  form  nerves.  A  nerve 
is  like  a  telegraph  cable.  It  consists  of  many  fibers, 
each  insulated  from  the  others.  Fibers  separate  from 
the  main  group  and  form  a  branch  of  the  nerve,  each 
having  a  particular  use.  Some  carry  messages  only  to 
the  brain  and  spinal  cord;  these  are  known  as  sensory 
m.n'es.  Others  carry  messages  from  the  brain  and  the 
spinal  cord  to  the  organs;  these  are  motor  nerves. 

The  brain.  Most  of  the  organs  of  our  body  are  in 
some  way  protected.  None,  however,  is  any  better 
protected  than  the  brain.  The  human  brain  is  an 
exceedingly  delicate  mechanism  and  would  be  subject 
to  frequent  injury  if  not  properly  protected.  It  is  pro- 
tected by  the  hair,  the  loose,  tough  scalp,  and  by  the  bones 
of  the  cranium.  The  arched  instep  and  the  curved  spinal 
column  give  some  "  spring "  to  the  body  and  hence  tend 
to  keep  the  brain  from  being  jarred.  Finally,  the  brain 
itself  is  enclosed  in  two  membranes. 

The  brain  is  the  largest  part  of  the  nervous  system. 
It  weighs  about  three  pounds  and  consists  of  a  mass 
of  nerv«'  c<ills  and  many  connecting  fibers.  It  maj  lxj 


386 


A  YEAR  IN  SCIENCE 


divided  into  three  regions:  fore  brain,  mid  brain,  and 
hind  brain.  The  latter  is  continuous  with  the  spinal 
cord. 

The  fore  brain  is  called  the  cerebrum.     It  is  enor- 
mously developed,  forming  about  three-fourths  of  the 


Spinal  Cord  . 

Fig.  178.     Side  view  of  the  brain. 

entire  brain,  and  is  divided  by  a  deep  fissure  into  a 
left  and  right  hemisphere.  Many  folds  and  ridges, 
called  convolutions,  greatly  increase  its  surface. 

The  mid  brain  is  an  isthmus  connecting  the  fore  and 
hind  brains. 

The  hind  brain  consists  of  the  cerebellum,  the  pens 
varolii,  and  the  medulla  oblongata.  The  cerebellum  has 
a  wrinkled  surface,  but  is  somewhat  different  in  appear- 
ance from  the  folded  cerebrum.  It  is  the  largest  part, 
of  the  hind  brain  and  is  partly  covered  at  the  back 
by  the  cerebrum. 

The  medulla  oblongata  lies  in  the  cranium,  but  it  is 


NERVOUS  SYSTEM  387 

really  the  enlarged  tipper  portion  of  the  spinal  cord. 
It  forms  a  connection  between  the  spinal  cord  and  the 
brain. 

The  pons  consists  of  broad  bands  of  nerve  tissue  that 
pass  around  the  ventral  side  of  the  medulla  and  connect 
the  two  halves  of  the  cerebellum. 

Twelve  pairs  of  nerves,  called  cranial  nerves,  arise 
from  the  brain.  These  are  distributed  to  different  parts 
of  the  head  and  to  the  body. 

Functions  of  brain.  The  functions  of  the  parts  of  the 
brain  are  as  follows: 

The  cerebrum  is  the  seat  of  all  sensations,  of  intelli- 
gence, of  memory,  of  emotions,  and  of  will.  Through 
it  we  receive  all  sensations  such  as  sight,  touch,  and 
taste,  and  in  it  originate  all  impulses  which  produce 
voluntary  movements. 

The  cerebellum  does  not  start  voluntary  motion  but 
it  coordinates  these  movements  and  makes  them  defi- 
nite. If  the  cerebellum  is  removed  from  a  pigeon,  for 
example,  the  pigeon  can  still  move  but  it  cannot  walk 
or  fly.  The  various  pairs  of  muscles  do  not  work 
together ;  those  of  the  right  side  do  not  work  with 
those  of  the  left.  Consequently  the  pigeon  nutters 
about,  but  it  can  make  no  definite  movements. 

The  medulla  is  a  passageway  for  impulses  between 
the  brain  and  the  spinal  cord. 

Spinal  cord.  The  large  nerve  which  passes  down 
through  the  backbone,  or  spinal  column,  is  called  the 
spinal  cord.  It  tapers  somewhat  at  the  lower  end,  but 


388 


A  YEAR  IX  SCIENCE 


its  average  diameter  is  about  three-fourths  of  an  inch. 
A  number  of  large  nerves,  thirty-one  pairs,  arise  from 
the  spinal  cord.  Their  branches  pass  to  all  parts  of 


Dorsal  Root 


White.. Matter 


Fig.  179.  Section  of  the  spinal  cord  showing-  the  method  of 
origin  of  the  spinal  nerves  by  two  roots.  The  arrows  indicate  the 
direction  in  which  the  nerve  impulses  pass  through  these  roots. 

the  body.  Each  of  these  nerves  has  two  roots.  The 
ventral  root  is  composed  of  fibers  which  carry  currents 
out  to  the  muscles  and  is,  therefore,  called  the  motor 
root.  The  dorsal  root  carries  currents  from  the  organs 
to  the  spinal  cord.  Consequently,  we  would  assume 
that  if  dorsal  roots  are  in  any  way  injured,  a  person 
would  lose  the  sensation  of  feeling  in  the  part  from 
which  these  nerves  led.  Similarly,  if  the  ventral  roots 
are  disabled  the  power  of  motion  would  be  lost. 
Experiments  on  lower  animals  or  observations  in 
human  beings  in  which  the  cord  has  been  injured,  or 
diseased,  confirm  these  assumptions. 

The  spinal  cord  is  of  great  importance;  first,  because 
it  relieves  the  brain  of  a  great  deal  of  work;  second, 
because  it  is  a  passageway  for  conducting  messages  of 


NERVOUS  SYSTEM  389 

importance  to  and  from  the  brain ;  and  third,  it  controls 
to  a  great  extent  the  digestive  and  the  circulatory 
systems. 

Sympathetic  nervous  system.  A  chain  of  ganglia  on 
each  side  of  the  spinal  column  together  with  three 
large  ganglia  and  a  network  of  nerves,  situated  in  the 
middle  line  of  the  body,  form  what  is  often  called  the 
sympathetic  nervous  system.  It  is  not  a  distinct  system 
at  all,  but  is  closely  connected  with  the  brain  and  the 
spinal  cord.  Nerves  from  these  centers  pass  to  many 
of  the  internal  organs,  to  the  skin,  to  the  glands,  and 
to  the  muscles.  This  system  also  relieves  the  brain,  for 
through  its  centers  many  of  the  involuntary  activities 
are  controlled.  One  of  these  centers,  located  just 
behind  the  pit  of  the  stomach,  is  the  so-called  "solar 
plexus."  A  blow  in  the  region  of  the  stomach  paralyzes 
many  parts,  and  may  even  result  in  instant  death. 

Action  of  nervous  system.  Even  the  simplest  motions 
which  we  perform  involve  the  action  of  many  nerves 
and  nerve  centers.  If  the  finger  is  accidentally  pricked 
by  a  pin,  a  touch  organ  in  the  skin  is  stimulated.  From 
this  currents,  or  impulses,  are  sent  over  several  nerve 
fibers  through  the  dorsal  root  into  the  spinal  cord. 
As  a  result  of  changes  which  this  produces  in  cells  in 
the  spinal  cord,  currents  are  sent  to  motor  cells  in  the 
cord.  From  these  motor  cells  currents  are  sent  over 
fibers  in  the  motor  root  to  a  muscle  in  the  arm.  This 
causes  a  contraction  of  the  muscle  which  produces  a 
motion,  the  response,  as  a  result  of  which  the  hand  is 


390  A  YEAR  IN  SCIENCE 

drawn  away  from  the  pin.  In  such  an  action  the 
current  is  carried  to  the  spinal  cord,  or  to  some  gan- 
glion, and  from  there  currents  are  sent  out  which  stimu- 
late the  muscles.  This  is  called  a  reflex  action. 

Reflex  actions.  These  actions  are  produced  without 
the  consent  of  any  conscious  center  of  the  brain.  The 
impulse  may  go  to  the  brain,  but  not  to  cells  where 
conscious  activity  occurs.  Reflex  actions,  such  as  the 
movements  of  the  internal  organs,  the  heart,  stomach, 
or  the  glands,  are  involuntary.  These  are  due  to  inter- 
nal stimuli.  Many  of  our  responses  to  external  stimuli 
are  also  reflex:  the  winking  of  the  eyelids,  walking, 
removing  the  hand  from  a  hot  object,  and  many  others. 
These  actions  are  performed  quickly,  and  they  also 
relieve  the  brain  of  a  great  deal  of  work.  All  of  our 
time  would  be  needed  to  attend  to  only  the  simplest 
activities  necessary  for  life,  if  they  were  all  done 
consciously. 

Voluntary  action.  We  have  just  learned  that  the 
peculiarity  of  a  reflex  movement  is  that  it  is  performed 
without  the  action  of  the  conscious  center,  the  cere- 
brum. All  actions  which  do  come  from  the  use  of  the 
cerebrum  and  which  are  thus  under  the  control  of  the 
will  are  voluntary. 

If  food  is  placed  before  us,  impulses  are  sent  from 
the  eye  to  the  visual  center  of  the  cerebrum.  From 
there  messages  may  be  sent  to  motor  centers  in  the 
brain,  from  which  in  turn  impulses  may  go  to  the 
muscles  of  the  arm  causing  us  to  pick  up  some  of  the 


NERVOUS  SYSTEM  391 

food.  It  is  not  necessary,  however,  for  us  to  eat  the 
food  after  it  is  in  the  mouth,  or  even  to  pick  it  up. 
We  may  decide  to  le^ve  it.  In  voluntary  actions,  the 
mind  controls  the  stimuli  which  are  sent  out. 

When  we  are  awake  countless  nerve  impulses  keep 
pouring  into  our  brains.  Of  some  of  these  we  are  con- 
scious, and  we  may  see,  hear,  or  taste.  The  impressions 
which  they  produce  are  more  or  less  lasting.  Some  are 
retained  for  only,  a  few  minutes,  but  others  may  be 
retained  for  years.  In  some  way  these  impressions  are 
stored  away  in  our  brains  and  constitute  our  memory. 

There  is  much  about  the  activity  of  the  nervous 
system  which  at  present  no  one  seems  to  know.  For 
example,  we  can  not  explain  exactly  how  nerve  cur- 
rents pass  along  the  nerves,  or  from  one  cell  to  another. 
We  often  compare  nerve  currents  with  electric  cur- 
rents. They  are,  however,  not  the  same.  Nerve 
currents  travel  only  about  one  hundred  feet  per  second ; 
electric  currents  travel  'thousands  of  times  more  rap- 
idly. Nerve  currents  wear  out  the  nerve  tissue;  elec- 
tricity seems  to  have  no  permanent  effect  on  the  wire 
over  which  it  passes.  We  likewise  do  not  know  just 
how  impressions  are  formed  in  our  brains,  or  how  they 
can  be  retained  there. 

Habits.  When  we  first  attempt  to  do  a  thing,  we 
do  it  slowly  and  awkwardly.  Each  time  we  repeat  the 
same  thing  we  do  it  more  rapidly  and  more  accurately. 
The  first  time  a  nerve  current  passes  over  a  certain  set 
of  nerves  and  through  certain  centers  it  does  so  slowly. 


392  A  YEAR  IN  SCIENCE 

At  each  repetition  of  the  same  act  the  currents  move 
more  rapidly.  For  this  reason  practice  makes  perfect. 
We  learn  to  write,  to  walk,  to  read,  to  think,  to  feel 
slowly  but  surely  as  the  nerve  routes  become  estab- 
lished. Finally  such  acts,  thoughts,  or  feelings  require 
little  attention,  and  we  speak  of  them  as  habits. 

Habits,  too,  save  the  brain  much  time  and  effort.  At 
first  the  mind  must  direct  each  impulse  necessary  to 
produce  the  movements  in  learning  to  write,  for 
example.  Later  on  these  impulses  reflexly  go  over  the 
proper  nerves  and  make  the  proper  connections. 

It  requires  considerable  effort,  wrhen  habits  are  once 
formed,  to  break  them.  Certain  impulses  readily  pass 
over  certain  nerves,  through  certain  centers,  and  pro- 
duce definite,  fixed  responses.  Only  with  great  and 
repeated  effort  is  it  possible  to  make  these  impulses 
travel  over  new  routes.  It  is  just  as  difficult  to  break 
a  good  habit  as  it  is  to  break  a  bad  one.  The  older 
we  grow  the  more  fixed  our  habits  become,  and  conse- 
quently the  more  difficult  to  change. 

It  is  wise  to  form  only  such  habits  of  thought  and 
action  as  will  make  us  most  useful  to  ourselves  and 
to  our  fellow-men.  The  importance  of  this  is  most 
forcibly  expressed  by  Professor  James : 

"The  hell  to  be  endured  hereafter,"  says  Professor 
James,*  "of  which  theology  tells,  is  no  worse  than  the 
hell  we  make  for  ourselves  in  this  world  by  habitually 
fashioning  our  characters  in  the  wrong  way.  Could 

*  Professor  James,  Psychology.    Henry  Holt  &  Co. 


NERVOUS  SYSTEM  393 

the  young  but  realize  how  soon  they  will  become  mere 
\ralking  bundles  of  habits,  they  would  give  more  heed 
to  their  conduct  while  in  the  plastic  state.  We  are 
spinning  our  own  fates,  good  or  evil,  and  never  to  be 
undone.  Every  smallest  stroke  of  virtue  or  of  vice 
leaves  its  never-so-little  scar.  The  drunken  Rip  Van 
Winkle,  in  Jefferson 's  play,  excuses  himself  for  every 
fresh  dereliction  by  saying,  1 1  won 't  count  this  time ! ' 
Well !  he  may  not  count  it,  and  a  .kind  Heaven  may  not 
count  it ;  but  it  is  being  counted  none  the  less.  Down 
among  his  nerve  cells  and  fibers  the  molecules  are 
counting  it,  registering  and  storing  it  up  to  be  used 
against  him  when  the  next  temptation  comes.  Nothing 
we  ever  do  is,  in  strict  scientific  literalness,  wiped  out. 
Of  course  this  has  its  good  side  as  well  as  bad  one. 
As  we  become  permanent  drunkards  by  so  many  sepa- 
rate drinks,  so  we  become  saints  in  the  moral,  and, 
authorities  in  the  practical  and  scientific  spheres  by 
so  many  separate  acts  'and  hours  of  work.  Let  no 
youth  have  any  anxiety  about  the  upshot  of  his  educa- 
tion, whatever  the  line  of  it  may  be.  If  he  keep  faith- 
fully busy  each  hour  of  the  working  day,  he  may 
safely  leave  the  final  result  to  itself.  He  can  with 
perfect  certainty  count  on  waking  up  some  fine  morn-,, 
ing,  to  find  himself  one  of  the  competent  ones  of  his 
generation,  in  whatever  pursuit  he  may  have  singled 
out," 

Education.     As    civilization    advances    success    and 
achievement  in  life  depend  more  and  more  upon  the 


394  A  YEAR  IN  SCIENCE 

ability  of  each  individual  to  use  his  brain,  but  in 
order  that  the  mind  may  act  quickly  and  easily  it  must 
be  trained.  Education  gives  this  training.  Through 
it  the  brain  not  only  obtains  information,  but  it  learns 
how  to  act  and  grow  stronger  by  use  just  as  the 
muscles  do.  Because  we  appreciate  how  important  this 
training  of  the  mind  is,  each  generation  spends  yearly 
millions  of  dollars  to  educate  the  young  people  who 
will  make  the  men  and  women  of  the  next  generation. 

Care  of  nervous  system.  Mens  sano  in  corpore  sano, 
a  sound  mind  in  a  sound  body,  is  just  as  true  to-day 
as  it  was  hundreds  of  years  ago  wThen  the  Greeks  and 
Romans  excelled  in  physical  and  in  mental  development. 
Everything  which  goes  to  build  up  a  sound  body  also 
builds  up  a  sound  mind.  Plenty  of  exercise,  fresh  air, 
work,  rest,  and  sleep  are  all  necessary  for  an  active 
brain. 

The  great  demands  made  upon  our  nervous  systems 
and  the  consequent  need  of  care  are  well  expressed  in 
the  following  quotation.  Mr.  Blount  says: 

"The  superiority  of  man  to  the  lower  animals  is 
most  conspicuous  in  his  nerve  system.  It  is  precisely 
where  civilized  man  is  most  developed  that  he  breaks 
down  most  easily.  We  live  in  what  has  been  called  an 
age  of  nervous  prostration.  The  speculator  watching 
the  market,  the  society  woman  madly  pursuing  a  pro- 
gram, and  the  scholar  striving  for  honors  or  promotion, 
all  are  the  frequent  victims  to  the  disease  of  the  age. 
We  should  learn  to  relax,  to  rest.  Some  time  each  day 


NERVOUS  SYSTEM  395 

should  be  given  to  quiet  and  meditation.  The  various 
sorts  of  mental  healing  often  produce  good  only  because 
they  establish  nerve  quiet,  and  direct  the  thoughts 
away  from  self.  One  can  live  under  good  conditions 
of  physical  hygiene,  and  yet  become  a  nervous  wreck, 
if  he  is  the  subject  of  constant  nervous  irritation. 
Great  minds  cultivate  poise  and  equanimity.  We  are 
wont  to  magnify  the  small  ills  of  life,  if  there  are  no 
large  objects  to  occupy  us.  One  engaged  in  thoughts 
of  science,  government,  or  philosophy  is  not  so  worried 
over  his  own  petty  affairs  of  life.  The  dignified  pur- 
suit of  a  worthy  object  in  life  gives  tone  and  poise  to 
the  nerve  system."* 

Questions 

1.  Why  would  it  be  impossible  for  us  to  live  with- 
out a  nervous  system? 

2.  What  is  the  structure  of  a  nerve  cell?     Of  a 
nerve  ? 

3.  How  does  a  motor  nerve  differ  from  a  sensory 
nerve  ? 

4.  Give  the  parts  of  the  brain. 

5.  Why    is    it    so    essential    that    the    brain    be 
protected? 

6.  Describe  the  cerebrum  and  state  its  functions. 

7.  How  does  the  cerebellum  differ  from  the  cere- 
brum   in    appearance    and    in    size?      What    is    its 
function  ? 

8.  How  is  the  brain   connected  with  the   spinal 
cord? 

*Blount,  Physiology  and  Hi/fiicne.     Row.  Peterson  &  Co. 


396  A  YEAR  IN  SCIENCE 

9.     What  is  the  function  of  the  medulla? 

10.  Give  the  size  and  location  of  the  spinal  cord. 

11.  Explain  how  a  spinal  nerve  is  attached  to  the 
spinal  cord. 

12.  What  is  the  difference  in  the  use  of  the  sensory 
root  and  the  motor  root? 

13.  What  is  the  sympathetic  nervous  system? 

14.  Trace  the  path  of  a  nerve  impulse  in  a  reflex 
action. 

15.  What   are  the   principal   advantages   in   reflex 
actions  ? 

16.  In  what  respects   do   voluntary   actions   differ 
from  reflex  ones  ? 

17.  What  is  the  physiological  reason  why  practice 
makes  perfect? 

18.  Why  is  it  an  advantage  in  early  life  to  form 
many  good  habits? 

19.  Point  out  the  error  in  thinking  that  we  can 
perform  a  certain  act  and  then  not  count  it. 

20.  Why  do  we  have  schools  ? 

21.  Learn  how  much  your  education  for  a  year  costs 
the   community  in  which  you  live.     Also,  determine 
how  much  it  costs  your  parents  to  keep  you  in  school 
for  a  year. 

22.  Is  the  education  which  you  are  receiving  worth 
that  amount  of  money  to  you? 

23.  Do   you    think   that    the    returns    which    your 
parents  and  the  community  are  receiving  are  adequate, 
considering  the   amount   of  money  which  they  have 
invested  in  your  education? 

24.  What  rest  and  care  do  you  give  your  nervous 
svstem? 


CHAPTER  XL VIII 
THE  SPECIAL  SENSES 

General.  It  is  quite  essential  that  we  receive  some 
very  definite  information  in  regard  to  the  world  out- 
side of  ourselves.  For  this  we  depend  upon  the  so- 
called  special  senses.  Originally  there  were  thought  to 
be  just  five  of  these,  feeling,  tasting,  smelling,  seeing, 
and  hearing.  To  these,  however,  we  must  add  some 
others,  especially  the  sense  of  temperature  and  of  pain. 
For  the  purpose  of  receiving  impressions  from  the  out- 
side world  and  then  of  converting  them  into  nerve  cur- 
rents we  have  highly  specialized  organs,  such  as  the  eye 
and  the  ear. 

Touch.  The  sense  of  touch  is  the  most  widely  dis- 
tributed of  the  special  senses,  for  all  parts  of  the  skin, 
the  tongue,  and  the  mucous  membrane  of  the  mouth 
and  nose  are  sensitive  to  touch.  In  the  dermis  of  the 
skin  there  are  many  minute  elevations  called  papillae. 
In  some  of  these  there  are  modified  structures  contain- 
ing the  ends  of  nerves  of  touch,  called  touch  corpuscles. 

In  some  parts  of  the  body  these  corpuscles  are  very 
close  together  so  that  the  sense  of  touch  is  keen.  In 
other  parts  they  are  far  apart  so  that  the  sense  of  touch 
is  dull.  The  degree  of  sensitiveness  of  the  various  parts 

397 


398  A  YEAR  IN  SCIENCE 

of  the  body  can  be  determined  by  the  use  of  a  compass.. 
If  the  person  operated  upon  has  his  eyes  closed  and 
the  compass  is  placed  on  the  back  of  the  neck  with  the 
points  three  inches  apart,  he  will  get  a  distinct  impres- 
sion of  each.  If,  however,  the  points  are  placed  from 
one  and  a  half  inches  to  two  inches  apart,  he  wdll  feel 
only  a  single  point.  On  the  tip  of  the  tongue  the  two 
points  can  be  distinguished  when  separated  only  one 
twenty-fourth  of  an  inch.  The  lips  and  finger  tips  are 
also  very  keen.  When  an  object  touches  the  skin  the 
pressure  upon  the  touch  corpuscles  stimulates  the  nerve 
endings  and  an  impulse  is  sent  to  the  brain. 

Temperature.  It  seems  safe  to  assume  that  the 
nerves  which  receive  the  impression  of  heat  and  cold 
are  not  the  same  as  those  used  for  touch.  When  the 
skin  is  touched  with  a  cold  object,  certain  areas  all 
over  the  body  give  us  a  sensation  of  cold.  Other  areas 
when  touched  with  a  warm  object  give  the  sensation 
of  warmth.  The  body  seems  to  be  mapped  out  into 
irregular  "cold  and  warm"  spots. 

Taste.  The  nerves  of  taste  end  in  taste  buds  which 
are  in  papillae  scattered  over  the  upper  surface  and 
sides  of  the  tongue,  the  pharynx,  and  in  parts  of  the 
soft  palate.  Hair-like  processes  project  from  the  taste 
cells  through  cavities  in  the  taste  buds.  These  proc- 
esses come  in  contact  with  the  food  which  must  be  in 
solution  to  be  tasted. 

There  are  four  different  kinds  of  tastes :  sweet,  sour, 
bitter,  and  salt.  All  parts  of  the  tongue  are  not  equally 


THE  SPECIAL  SENSES  399 

sensitive  to  each  of  them.  The  bitter  taste  is  most 
developed  at  the  back  of  the  tongue,  the  sour  at  the 
sides,  the  sweet  at  the  tip,  and  the  salt  taste  is  nearly 
equally  distributed.  Many  of 
our  tastes  are  combinations 
of  these  four  primary  ones 
together  with  smell. 

Smell.     The  sense  of  taste 
and  smell  at  the  beginning  of 
the    digestive   tract   and   the 
sense  of  smell  at  the  begin- 
ning of  the  respiratory  tract 
also  will   at   once  suggest   a        TiB'  180'    The  tonsue' 
possible  function  for  these  two  senses.     They  are  un- 
doubtedly of  some  use  in  helping  us  to  detect  unfit  food 
and  air. 

The  nerves  of  smell,  the  olfactory  nerves,  have  their 
endings  in  the  mucous  membrane  of  the  upper  part  of 
the  nasal  cavity.  Substances  which  stimulate  these 
nerves  give  off  small  particles  which  are  then  carried 
into  the  nose  by  currents  of  air.  The  sense  of  smell 
is  not  so  keen  in  man  as  it  is  in  dogs,  or  in  some  other 
lower  animals.  Even  in  man  it  is  very  acute,  but  it 
becomes  exhausted  rather  quickly. 

Eye.  The  eyes  are  delicate,  complex,  nearly  spherical 
bodies  which  fit  into  sockets  formed  by  the  facial 
bones.  They  are  further  protected  by  folds  of  skin, 
the  eyelids.  They  are  freed  of  dust  and  kept  moist 
by  mucus  and  by  tears  secreted  by  the  tear  glands. 


400  A  YEAR  IN  SCIENCE 

A  tear  gland  is  located  on  the  outer  and  upper 
side  of  each  eye.  The  fluid  secreted  by  this  gland 
passes  over  the  eye  and  is  carried  away  by  a  duct,  of 
Avhich  one  branch  opens  on  the  inner  angle  of  the  lower 
eyelid,  and  another  opens  in  the  upper  eyelid.  The 
other  end  «f  this  duct  opens  into  the  nasal  passage. 

The  eyeball  is  held  in  place  and  moved  by  six  muscles. 
One  end  of  these  muscles  is  attached  to  the  eyeball, 
and  the  other  end  at  the  back  part  of  the  bony  socket 
into  which  the  eye  fits.  One  set  of  these  muscles  turns 
the  eye  toward  or  away  from  the  nose.  A  second  set 
turns  the  eyeball  upward  or  downward.  The  third  set 
of  oblique  muscles  rotates  the  eyeball. 

Structure.  The  eye  is  made  up  of  three  layers  or 
coats.  The  outer  coat  is  opaque  and  white,  forming 
the  " white  of  the  eye."  It  is  known  as  the  sclerotic 
layer.  It  is  a  tough  strong  coat  filled  with  blood  ves- 
sels. At  the  front  this  layer  becomes  transparent  and 
forms  the  cornea. 

Inside  of  the  sclerotic  layer  is  the  choroid  coat,  which 
is  colored  black.  In  front  it  is  usually  brown  or  blue 
and  forms  the  iris.  In  the  center  of  the  iris  is  an  open- 
ing, the  pupil.  This  is  controlled  by  muscles  which 
open  or  close  it. 

The  innermost  coat,  the  retina,  covers  the  back  por- 
tion of  the  choroid  coat.  It  is  a  very  complex  mem- 
brane, and  in  it  are  the  endings  of  the  optic  nerve 
which  enters  the  eye  at  the  back. 

Just  back  of  the  pupil  is  the  crystalline  lens.    Between 


THE  SPECIAL  SENSES 


401 


it  and  the  cornea  is  a  space  filled  with  a  transparent 
watery  fluid,  the  aqueous  humor.  The  entire  cavity  of 
the  eyeball  back  of  the  lens  is  filled  with  a  jelly-like 
mass,  the  vitreous  humor. 

.  Sclerotic 


Choroid 


Cornea 


Aqueous 
humor 


Fig.   181.     Section-  of  the  eye. 

Light.  The  nerve  endings  in  the  retina  when  stimu- 
lated by  light  start  impulses  to  the  brain  which  produce 
sensations  of  sight.  The  source  of  this  light  varies. 
It  may  be  the  sun,  an  electric  light,  or  it  may  be  light 
reflected  by  objects. 

We  can  not  give  a  definite  answer  to  the  question, 
"What  is  light?"  We  do  know  how  to  produce  it, 
and  we  do  know  many  things  about  its  behavior.  It 
is  supposed  that  vibrations,  or  light  waves,  are  given 
off  in  all  directions  by  luminous  bodies.  These  waves 
travel  in  straight  lines ;  a  single  line  of  light  is  called  a 


402  A  YEAR  IN  SCIENCE 

ray.     Light  travels  at  a  velocity  of  about  one  hundred 
and  eighty-six  thousand  miles  per  second. 

When  light  rays  strike  a  body,  one  of  three  things 
happens  to  them:  they  may  enter  the  body  and  stop, 
they  may  strike  its  surface  and  bound  back,  or  they 
may  go  through  it.  If  they  stop  in  the  substance  we 
say  they  are  absorbed;  if  they  bound  back  we  say  they 
are  reflected.  If  light  passes  through  one  substance  from 
another,  the  light  waves  are  often  bent  out  of  a  straight 
line.  To  this  change  of  direction  we  give  the  name 
refraction. 

Lenses.  When  light  passes  from  air  through  glass 
it  is  refracted.  For  purposes  of  refraction  a  piece  of 
glass  with  one  or  two  curved  surfaces  is  frequently 

used.    This  is  called  a  lens. 
Lenses    are     of    different 
forms  as  shown  in  Figure 
Concav^  182.     When  rays  of  light 

pass    through    a    concave 
lens,     they    spread    away 
Fig.   182.     A  biconvex  and  a     from    each    other.      When 

biconcave  lens. 

they  pass  through  a  convex 

lens,  they  are  brought  toward  each  other  and  meet  at 
a  point  called  the  focus. 

In  the  eye  the  cornea  and  the  lens  have  convex 
surfaces.  When  an  object  is  seen,  rays  of  light  pass 
from  every  point  of  it  through  the  cornea  and  the  lens, 
and  are  brought  to  a  focus  on  the  retina  where  an  image 
of  the  object  is  formed. 


THE  SPECIAL  SENSES 


403 


Images.    When  a  lens  is  used  to  form  an  image,  it  is 
always  desired  that  a  distinct  image  be  formed  on  a 


F:: 


Yig.  183.     A  biconvex  lens  bending  the  rays  of  light  so  as  to  bring 
them  to  a  point,  the  focus. 


given  surface.  If  a  candle  is  placed  in  front  of  a  con- 
vex lens,  and  a  screen  is  placed  back  of  the  lens  and 
moved  back  and  forth,  a  place  will  be  found  at  which 
a  sharp  but  inverted 
image  of  the  candle 
is  thrown  upon  the 
screen. 

Focusing.     In  the 
experiment  above,   it 
evident    that    the 


IS 


Fig.  184.  Diagram  showing  the 
method  of  the  formation  of  an  image 
by  a  lens. 


screen  must  be  placed 
in  a  certain  position  if  a  distinct  image  is  produced.  In 
a  camera  the  image  of  the  object  falls  upon  the  sensi- 
tive plate  or  film.  To  secure  this  for  any  given  object, 
the  lens  in  the  camera  must  be  moved  backward  and 
forward  until  the  converging  rays  are  brought  to  a 
focus  on  the  plate. 

In  the  eye,  the  distance  between  the  lens  and  the 
retina   can   not  be  changed,   consequently  the  focusing 


404 


A  YEAR  IN  SCIENCE 


must  be  done  in  a  different  way.  It  is  brought  about 
by  a  change  in  the  shape  of  the  lens.  The  lens  is  elastic, 
and  if  left  to  itself  it  tends  to  become  more  convex. 
It  is  fastened  to  the  choroid  coat  by  a  ligament,  known 


Fig-.    185.      Diagram   of   the   eye   showing-   the   convex   lens   forming 
an  image  by  converging  the  rays  on  the  retina. 

as  the  suspensory  ligament.  This  is  ordinarily 
stretched  tight  and  exerts  a  constant  pull  on  the  lens, 
tending  to  make  it  thinner.  By  means  of  ciliary  mus- 
cles the  choroid  coat  can  be  drawn  forward.  This 
loosens  the  suspensory  ligament  and  the  lens  becomes 
more  convex.  This  power  of  the  eye  to  change  the 
curvature  of  the  lens  is  called  accommodation. 

The  more  convex  the  lens  is,  the  more 
it  bends  the  rays  of  light.  When  an 
object  is  near,  the  light  rays  from  any 
point  of  it  spread  out  or  diverge  rapidly. 
To  bring  these  to  a  focus  they  must  be 
bent  very  decidedly.  This  can  be  done 
when  the  lens  is  convex.  Light  from  a 
distant  object  comes  to  us  almost  paral- 

Fig.  186.    Dia- 

frate  changes^     lel  ancl  nence  a  flattened  lens  can  bring 

the    lens    in    ac-       •.  £ 

commodation.  it  to  a  IOCUS. 


THE  SPECIAL  SENSES  405 

Defects  of  the  eye.  There  are  several  defects  of  the 
eye  which  are  common:  short  sight edness,  far  sight  ed- 
ness,  and  astigmatism.  Spectacles  are  worn  to  compen- 
sate for  these  defects.  In  a  near  sighted  eye,  objects 
can  be  seen  distinctly  only  when  not  more  than  about 
ten  inches  away.  If  an  object  is  at  a  greater  distance, 
the  focus  is  formed  in  front  of  the  retina.  To  remedy 
this  defect  concave  lenses  are  used.  These  will  throw 
the  image  farther  back  upon  the  retina. 

If  the  eye  is  far  sighted,  the  image  will  fall  behind 
the  retina  unless  the  object  is  more  than  ten  inches 
away.  To  correct  this  convex  glasses  are  used.  These 
Avill  bring  the  focus  farther  forward. 

Astigmatism  is  a  very  common  defect  in  the  eye. 
This  is  due  to  an  irregular  curvature  in  the  surfaces 
of  the  cornea  or  lens,  or  in  both.  The  result  is  that 
only  a%  part  of  the  rays  focus  on  the  retina  at  once. 
This  produces  a  blurred  image.  The  eye  muscles 
become  strained  in  trying  to  adjust  the  lens  to  secure 
a  clear  image.  As  a  result  headaches  are  frequently 
produced. 

Care  of  the  eyes.  Too  much  care  can  not  be  taken 
of  the  eye;  first,  because  the  eye  is  a  very  delicate 
instrument,  and  second,  because  it  is  so  very  useful 
to  us.  Frequently  defects  of  the  eye  escape  the  atten- 
tion. This  is  especially  true  in  children.  Nervousness 
and  headaches  are  often  caused  by  defective  vision.  If 
glasses,  properly  fitted  by  a  competent  oculist,  are 
worn,  these  troubles  may  be  relieved.  The  light  by 


406  A  YEAR  IN  SCIENCE 

which  we  read  should  be  good,  but  not  too  bright;  it 
should  come  from  above  or  from  one  side.  Care  should 
be  taken  to  avoid  having  bright  lights  shine  directly 
into  the  eyes,  or  having  it  reflected  into  them  from  the 
page.  A  flickering  light  is  very  tiresome.  Reading  in 
the  cars  is  extremely  taxing  because  the  eye  is  strained 
in  trying  to  follow  the  book  which  is  constantly  being 
moved  by  the  jarring  of  the  car.  The  distance  at 
which  a  book  should  be  held  will  vary  somewhat,  but 
twelve  to  fifteen  inches  is  the  best  distance  for  steady 
reading. 

The  eyes  should  not  be  rubbed,  for  they  might 
become  infected  by  germs  on  the  fingers.  Dust  is  also 
bad  for  the  eyes.  It  sometimes  contains  harmful 
germs,  and  it  always  irritates  them.  A  saturated  solu- 
tion of  boracic  acid  is  best  for  washing  inflamed  eyes. 

The  ear.  If  a  bell  is  struck,  it  is  made  to  vibrate. 
This  causes  the  air  in  all  directions  around  the  bell 
to  vibrate,  and  waves  of  sound  are  produced.  Some  of 
these  waves  of  sound  enter  the  ear,  are  conducted  through 
the  ear,  and  finally  stimulate  the  ends  of  the  auditory 
nerve  from  which  nerve  currents  are  sent  to  the  brain. 

Structure  of  the  ear.  The  ear  is  divided  into  three 
parts :  the  external,  the  middle,  and  the  internal  ear. 

1.  The  external  ear  consists  of  the  oval,  more  or 
less  flattened  structure  at  the  side  of  the  head.  It  is 
composed  of  cartilage  and  skin.  It  collects  sound 
waves  and  helps  to  converge  them  into  the  auditory 
canal  which  is  the  tube  leading  to  the  middle  ear. 


THE  SPECIAL  SENSES  407 

Across  the  inner  end  of  this  tube  is  stretched  a  thin 
membrane  known  as  the  car  drum. 


Fig.  187.     Diagram  to  illustrate  the  structure  of  the  ear. 

2.  Beyond  the  ear  drum  is  a  small  cavity  in  the 
temporal  bone.  This  is  the  middle  ear.  It  is  connected 
with  the  pharynx  by  the  Eustachian  tube.  Through 
this,  air-  enters  the  middle  ear  and  presses  on  the  inside 
of  the  ear  drum,  balancing  the  pressure  of  the  air  on 
the  outside  of  the  drum.  A  sudden  very  loud  noise 
might  otherwise  burst  the  ear  drum  because  of  the 
great  pressure  outside.  There  are  three  bones  in  the 
middle  ear;  the  hammer,  the  anvil,  and  the  stirrup. 
These  small  bones  are  arranged  in  a  chain  across  the 
cavity  of  the  middle  ear.  The  first  is  connected  with 
the  ear  drum  and  the  third  is  fastened  to  a  membrane 
over  an  opening  into  the  internal  ear. 


408  A  YEAR  IN  SCIENCE 

3.  The  internal  ear  is  far  more  complex  than  the 
other  parts.  It  is  an  irregular  cavity  in  the  temporal 
bone  lined  with  a  membranous  sac.  Lying  next  to  the 
middle  ear  is  a  tube  coiled  like  a  snail  shell  and  called 
the  cochlea.  Next  to  this  there  is  a  central  portion 
back  of  which  there  are  three  semicircular  canals  lying 
in  three  planes  and  placed  perpendicular  to  each  other. 
All  of  these  tubes  are  filled  with  a  watery  fluid.  In 
the  cochlea  is  a  thin  membrane  in  which  the  auditory 
nerves  terminate. 

Action  of  ear.  The  external  ear  gathers  the  sound 
waves  so  that  they  pass  down  the  auditory  canal  to  the 
ear  drum.  This  then  starts  to  vibrate.  These  vibrations 
pass  through  the  three  bones  of  the  middle  ear  to  the 
membrane  separating  it  from  the  internal  ear.  From 
this  membrane  the  liquids  in  the  middle  ear  are  set  in 
motion.  They  in  turn  cause  the  membrane  in  the 
cochlea  to  vibrate  and  thus  stimulate  the  nerves  from 
which  impulses  are  sent  to  the  brain. 

It  is  generally  supposed  that  different  parts  of  this 
membrane  respond  to  different  rates  of  vibration  and 
this  makes  it  possible  for  us  to  distinguish  between 
different  pitches.  The  range  of  hearing  is  very  great. 
We  can  hear  sounds  corresponding  to  vibrations  from 
about  30  to  about  40,000  per  second.  Between  these 
limits  as  many  as  6,000  variations  of  pitch  can  be 
perceived. 

The  semicircular  canals  are  not  used  for  hearing. 
They  are  used  in  maintaining  the.  balance,  or  equilib- 


THE  SPECIAL  SENSES  409 

rium,  of  the  body.  Through  them  we  know  in  what 
position  the  body.  is.  Even  with  our  eyes  closed,  we 
know  in  what  direction  the  body  is  leaning  and  how 
to  move  to  balance  it. 

Care  of  ears.  Since  the  middle  and  inner  ears  are 
enclosed  in  bone  there  is  very  little  danger  of  injuring 
them.  By  attempting  to  remove  the  ear  wax  from  the 
external  ear  injury  is  sometimes  done  to  the  ear  drum. 
This  wax  is  a  protection  against  insects  entering  the 
ear.  It  should  not  be  removed  except  with  clean  warm 
water. 

In  severe  colds  the  ear  may  become  infected  by 
germs  passing  up  through  the  Eustachian  tubes.  This 
sometimes  causes  very  serious  infections  in  the  ear;  in 
the  porous  bones  around  the  head ;  and,  in  extreme  cases, 
it  may  extend  to  the  brain.  In  any  such  infection  a 
physician's  services  are  necessary. 


Questions 

1.  Name  seven  senses. 

2.  Of  what  use  are  the  sense  organs? 

3.  Name  the  senses  having  organs  located  in  the 
skin. 

4.  Are  all  parts  of  the  skin  equally'  sensitive  to 
touch  ? 

5.  Describe  the  sense  organs  of  taste. 

6.  Where  is  the  sense  of  smell  located? 

7.  If  you  have  a  cold  Avhy  is  it  difficult  to  taste 
some  substances? 


410  A  YEAR  IN  SCIENCE 

8.  How  is  the  eyeball  protected? 

9.  Name  and  describe  the  parts  of  the  eye. 

10.  What  is  the  nature  of  light? 

11.  Explain   how   the    rays    of   light    are   bent   in 
passing  through  a  convex  lens. 

12.  "What  is  an  image?    Where  must  the  image  fall 
in  the  eye  if  the  object  is  seen? 

13.  Explain  what  is  meant  by  accommodation. 

14.  How  may  shortsightedness  and  farsightedness 
be  remedied? 

15.  What  is  astigmatism? 

16.  Give  some  points  in  reference  to  the  care  of  the 
eyes. 

17.  What  is  the  structure  of  the  external  ear  ?    The 
middle  ear?    The  internal  ear? 

18.  What  is  the  nature  of  sound? 

19.  How  are  sound  waves  transmitted  through  the 
ear  to  the  auditory  nerve? 

20.  Of  what  use  are  the  semicircular  canals? 

21.  Why  do  colds  sometimes  affect  the  ear! 


CHAPTER  XLIX 
HEALTH  AND  DISEASE 

Importance  of  health.  Physical  health  is  essential 
to  the  greatest  success  and  happiness  of  any  individual. 
Likewise,  the  prosperity  of  any  community  depends 
upon  the  health  of  the  community,  which  is  the  com- 
bined health  of  its  individuals.  The  preservation  of 
health,  both  individual  and  public,  is  an  important  duty. 
In  order  to  fulfill  this  duty,  imposed  upon  each  one  of 
us,  it  is  necessary  to  understand  the  conditions  which 
make  for  disease  as  well  as  those  which  make  for  health. 
The  science  of  keeping  the  body  in  good  health  is 
called  hygiene. 

Health  and  disease.  We  already  know  that  each 
organ  in  the  body  has  a  special  work  to  do.  It  is 
also  true  that  each  tissue  and  even  each  cell,  has  certain 
functions  to  perform.  If  the  various  activities  of  all 
of  the  cells  are  being  properly  performed,  we  are  in 
good  health.  If  anything,  however,  interferes  with  the 
functions  of  these  cells  so  that  they  are  not  properly 
performed  disease  results. 

Cause  of  disease.  Diseases  are  due  to  many  causes, 
some  of  which  are  known,  and  some  of  which  are  still 
unknown.  The  causes  of  some  diseases  are  very  evi- 
dent; for  example,  an  accident  may  deprive  a  man  of 

411 


412  A  YEAR  IN  SCIENCE 

his  arm  or  injure  some  internal  organ.  Parasites,  such 
as  the  tapeworm,  or  trichina,  may  infest  organs  and 
thus  interfere  with  their  working. 

In  many  diseases  the  causes  are  not  so  evident,  but 
we  .now  know  that  they  are  the  result  of  the  action  of 
very  small  plants  and  animals.  They  are  commonly 
called  bacteria,  germs,  micro-organisms,  or  microbes. 
These  small  organisms  either  act  directly  upon  the  tis- 
sues, or  they  produce  poisons,  called  toxins,  which 
destroy  the  tissues  or  in  some  other  way  prevent  their 
.normal  activity. 

The  more  common  plant  germs,  we  have  already 
learned,  are  bacteria.  Diseases  of  which  we  know  they 
are  the  cause  are  diphtheria,  measles,  tuberculosis, 
pneumonia,  mumps,  scarlet  fever,  tetanus  (lock  jaw), 
cholera,  plague,  and  spinal  meningitis.  Small  one- 
celled  animals,  protozoa,  are  likewise  responsible  for 
some  diseases,  the  best  known  of  which  are  malaria, 
smallpox,  and  yellow  fever.  All  diseases  which  are 
caused  by  germs  are  "catching"  or  contagious. 

How  germs  enter  the  body.  Germs  are  found  every- 
where about  us,  in  the  air,  in  the  water,  in  our  food, 
and  on  our  clothing.  Fortunately,  not  all  of  them 
succeed  in  entering  the  body,  and  even  if  some  of  them 
do  get  in  they  do  not  always  find  conditions  there 
favorable  to  growth. 

Germs  must  enter  the  body  through  the  digestive 
tract,  the  respiratory  organs,  or  the  skin.  Those  which 
enter  the  digestive  tract  are  taken  in  with  our  food 


HEALTH  AND  DISEASE  413 

and  Avater,  or  they  can  enter  the  mouth  through  the 
air.  Many  enter  this  way,  chief  of  which  cause  typhoid 
fever,  cholera,  and  dysentery. 

The  respiratory  organs  afford  the  best  entrance  to 
the  body  for  germs.  This  is  primarily  because  germs 
are  so  easily  carried  by  air.  In  spite  of  the  many 
adaptations  of  the  respiratory  organs  for  the  removal 
of  dust  and  germs,  the  long  irregular  passageways  are 
good  lodging  places  for  them.  Tuberculosis,  pneu- 
monia, colds,  influenza,  tonsilitis,  bronchitis,  and  many 
other  diseases  enter  the  body  in  this  way. 

Fortunately  the  skin  is  a  very  effective  covering  of 
the  body,  and  it  consequently  prevents  the  entrance  of 
foreign  material.  If  the  skin  is  removed  in  any  way, 
as  in  cuts  or  other  injuries,  germs  can  then  enter. 
Those  which  produce  blood  poisoning  enter  the  body  in 
this  manner.  Diseases  such  as  malaria,  yellow  fever, 
or  bubonic  plague  are  communicated  to  man  by  the 
bites  of  insects  and  thus  enter  the  body  through  the 
skin. 

Growth  of  germs.  When  germs  have  entered  the 
body,  they  sometimes  find  there  conditions  favorable 
for  their  growth;  plenty  of  food  and  moisture,  and  a 
warm  temperature.  A  few  will  grow  any  place  in 
the  body,  but  most  of  them  show  some  choice  in  their 
selection  of  these  favorable  conditions.  Some  will 
grow  only  in  the  respiratory  tract,  others  in  the  ali- 
mentary canal,  and  still  others  only  in  the  blood  or 
skin. 


414  A  YEAR  IX  SCIENCE 

A  number  of  days  elapse  from  the  time  the  germs 
enter  the  body  until  they  exist  in  sufficient  numbers 
for  the  disease  to  appear.  This  time  is  known  as  the 
incubation  period.  The  length  of  this  period  varies  with 
the  kind  of  disease.  For  measles  it  is  nine  days,  scarlet 
fever  two  to  four  days,  typhoid  fever  two  weeks,  and 
grippe  from  one  to  five  days. 

How  the  body  destroys  germs.  In  spite  of  these 
innumerable  and  active  enemies/  the  body  is  generally 
well  able  to  defend  itself.  It  has  at  least  three  means 
of  destroying  germs;  by  the  white  Hood  corpuscles, 
by  substances  called  germicides,  and  by  other  .sub- 
stances called  antitoxins. 

1.  White  corpuscles.    We  have  already  referred  to 
the  method  by  which  the  white  blood  corpuscles  destroy 
germs.     They  are  present  not  only  in  the  blood,  but 
also  in  all  parts  of  the  body.    If  bacteria  are  present, 
they  surround  and  *  destroy  them.     The.y  are   always 
present  in  great  numbers  around  a  wound. 

2.  Germicides.     In    the    blood    there    are    certain 
unknown    substances    formed    which    destroy    germs. 
They   are   called   germicides.     If   these   substances   are 
present  in  sufficient  quantities  in  the  blood,  they  kill 
the  disease  germs  and  consequently  protect  the  body 
from  disease. 

3.  Antitoxins.     The  injurious  effects  of  disease  are 
sometimes    the    result    of    poisons,    toxins,    which    the 
germs  produce.     There  is  sometimes  produced  in  the 
body  a  substance  called  antitoxin  (anti,  against).    This 


HEALTH  AXD  DISEASE  415 

counteracts,  or  acts  against,  the  toxin  so  as  to  render 
it  harmless.  Each  disease  probably  has  its  own  anti- 
toxin. If  this  is  produced  rapidly  and  abundantly 
enough,  the  toxin  of  any  disease  is  destroyed,  the  cof- 
puscles  then  dispose  of  the  germs,  and  there  is  imme- 
diate recovery  from  the  disease. 

If  the  body  is  kept  in  good  healthy  condition  by  the 
proper  food,  exercise,  and  plenty  of  fresh  air  and 
sleep,  there  is  usually  an  abundance  of  white  corpus- 
cles to  defend  it  against  germs.  It  is  also  in  the  proper 
condition  to  produce  the  right  germicides  or  antitoxins, 
and  thus  render  it  less  subject  to  infectious  diseases. 

Treatment  of  disease.  To  cure  an  infectious  disease 
it  is  necessary  to  destroy  the  germs  which  produce  it. 
The  power  to  do  this  lies  mostly  in  the  body  itself. 
If  it  becomes  impossible  for  the  body  to  accomplish 
this,  however,  other  means  must  be  resorted  to.  Chief 
of  these  are  serums,  vaccines,  and  drugs  which  we  call 
medicines. 

Serums  are  obtained  from  the  blood  of  an  animal, 
usually  a  horse.  They  are  prepared  in  the  following 
manner :  dead  or  weakened  germs,  or  the  toxins  of  the 
diseases  to  be  cured,  are  injected  into  the  blood  of  the 
horse.  "We  still  have  much  to  learn  in  regard  to  the 
substances  which  these  then  produce  in  the  blood  of 
the  animal.  Extracts,  called  serums,  are  made  from 
the  blood  drawn  from  an  animal  treated  in  this  way. 
"We  do  know,  however,  that  if  such  serums  are  injected 
into  a  person,  substances  are  produced  which  result 


416  A  YEAR  IN  SCIENCE 

in    the     destruction    of    the     disease     germs    in    the 
person. 

One  of  the  most  recent  and  valuable  discoveries  in 
medicine  is  the  method  of  production  and  the  use  of 
serums  called  antitoxins  which  normally  are  produced 
in  the  blood  of  a  person  who  has  an  infectious  disease. 
The  immediate  stimulus  for  their  production  is  the 
presence  of  toxins.  Sometimes  these  are  not  produced 
rapidly  enough  and  the  disease  cannot  be  checked.  For 
a  few  diseases,  such  as  diphtheria  and  lock  jaw,  it  has 
been  found  possible  to  produce  artificial  antitoxins  to 
inject  into  the  human  body.  The  method  for  producing 
the  antitoxin  for  diphtheria  is  as  follows:  Bacteria 
which  produce  diphtheria  are  grown  in  blood  serum  in 
the  laboratory.  These  bacteria  produce  toxins,  which  are 
then  separated  from  the  live  germs.  A  number  of  doses 
of  this  toxin  are  then  injected  into  the  blood  of  a  horse. 
This  is  done  at  intervals  for  several  months,  during 
which  time  large  quantities  of  antitoxin  are  being  pro- 
duced in  the  horse's  blood.  Finally  blood  is  taken  from 
the  horse  and  from  it  antitoxin  is  extracted.  This  is 
injected  into  the  body  of  a  person  who  has  diphtheria 
and  often  causes  a  cure.  If  it  is  injected  into  the  body 
of  a  person  who  has  been  exposed  to  the  disease,  it  pre- 
vents its  development. 

Vaccines.  The  term  vaccine  is  familiar  to  most  of 
us  because  of  its  long  use  in  connection  with  vaccina- 
tion for  smallpox.  In  order  to  stimulate  the  body  to 
produce  substances  to  destroy  a  disease,  dead  or  weak- 


HEALTH  AND  DISEASE  417 

ened  germs  of  that  disease  are  sometimes  'injected  into 
the  body. 

Vaccination  (vacca,  cow)  was  discovered  in  1796  by 
Jenner.  He  found  at  that  time  that  if  pus  from  sores 
found  on  cows,  suffering  from  the  disease  cowpox,  was 
injected  into  the  human  body,  the  person  was  pro- 
tected from  smallpox. 

The  methods  at  first  employed  in  securing  this  pus, 
or  vaccine,  were  very  crude  and  the  results  from  its 
use  were  sometimes  disastrous.  It  is  now  secured  by 
injecting  into  a  healthy  young  cow  germs  which  give 
the  cow  the  disease  known  as  cowpox.  This  results 
in  the  formation  of  sores  from  which  pus  is  taken. 
It  is  preserved  in  small  tubes  and  is  injected  into  the 
skin  when  a  person  is  vaccinated.  If  this  l  '  takes, '  '  the 
person  has  a  mild  disease  which  produces  in  the  blood 
germicides  for  the  smallpox  germ.  Vaccination  is  now 
being  successfully  carried  out  against  typhoid  fever. 
This  is  done  in  cases  of  epidemics  in  cities,  and  also 
in  armies. 

Medicines.  Very  few  drugs  can  be  used  to  destroy 
germs.  Those  which  are  successful  are  in  most  cases 
also  destructive  to  the  tissues.  Physicians  give  medi- 
cines to  aid  the  body  in  the  destruction  of  the  germs, 
the  substances  for  which  must  come  from  the  body 
itself.  In  some  cases  medicines  are  administered  to 
produce  immediate,  but  only  temporary,  relief.  This 
does  not  cure  the  disease,  but  it  is  often  an  advantage. 
To  accomplish  such  relief  drugs  are  sometimes  used  to 


418  A  YEAR  IN  SCIENCE 

i 

benumb  the  nerves;  hot  or  cold  applications,  or  elec- 
tricity may  also  be  used. 

In  a  few  instances,  it  is  possible  to  destroy  the 
germs  directly.  This  is  true  for  germs  in  the  throat, 
nose,  and  skin  where  they  can  be  reached  and  destroyed 
by  antiseptics. 

It  is  most  essential  that  every  one  realize  the  neces- 
sity of  putting  a  sick  person  into  the  hands  of  a 
competent  physician.  Home  remedies  are  seldom  bene- 
ficial, and  they  are  often  harmful.  Discretion  is  neces- 
sary in  the  selection  of  a  physician,  for  he  must  be 
honest  as  well  as  skillful  and  well-trained.  We  may 
always  be  certain  that  a  physician  who  advertises  is 
not  reliable.  Many  efforts  have  been  made  in  the  past 
few  years  to  protect  the  public  against  " quack" 
doctors  wTho  profess  to  have  some  secret  cure  for  dis- 
eases. However,  there  are  still  thousands  of  these 
incompetent  practitioners  operating  all  over  the  coun- 
try. By  foul  means  and  under  false  pretenses  they  get 
their  patients '  money. 

In  the  same  class  with  " quack"  doctors  must  be 
placed  many  patent  medicines.  Some  of  these  medicines 
are  good,  and  especially  so  when  taken  under  the 
direction  of  a  physician.  Many,  however,  are  not  only 
useless,  but  they  are  also  harmful,  frequently  contain- 
ing alcohol  and  other  harmful  drugs.  Headache  tablets, 
in  particular,  often  contain  opiates.  Death  sometimes 
results  from  their  use.  The  alcohol  in  patent  medicines 


HEALTH  AND  DISEASE  419 

produces  a  temporary  exhilaration  which  is  often  mis- 
taken for  some  beneficial  effect. 

Immunity.  In.  some  cases 'germs  may  enter  the  body 
of  an  individual  and  yet  have  no  effect  on  him.  He 
is  said  to  be  immune  to  that  disease.  This  immunity, 
undoubtedly,  depends  upon  the  presence  of  substances 
in  the  body  which  can  destroy  the  germs.  We  already 
know  that  certain  diseases,  such  as  mumps,  smallpox, 
and  whooping  cough,  we  do  not  have  a  second  time.  On 
the  other  hand,  some  diseases  recur  time  and  again.  It 
is  not  definitely  known  just  why  this  difference  exists. 
Evidently  the  antitoxin,  germicide,  or  other  substance 
which  was  produced  to  cure  a  given  disease  remains 
in  the  body  for  a  more  or  less  definite  period  of  time. 
In  some  diseases  this  is  for  life. 


Questions 

1.  Why  should  we  know  something  about  hygiene  ? 

2.  What  are  the  principal  causes  of  disease? 

3.  Name  eight  diseases  caused  by  germs. 

4.  HOAV  do  germs  enter  the  body  ? 

5.  Explain  the  incubation  period  of  a  disease. 

6.  What  are  the  ways  in  which  the  body  defends 
itself  against  the  attack  of  germs? 

7.  How  are  serums  obtained? 

8.  Of  what  value  are  antitoxins?     How  are  they 
produced? 

9.  Why  has  it  been  possible  to  reduce  the  death 
rate  of  smallpox? 


420  A  YEAR  IN  SCIENCE 

10.  Why  should   we   place  no   confidence   in  phy- 
sicians who  advertise? 

11.  Discuss  the  value  of  patent  medicines. 

12.  What  do  you  understand  by  the  term  immunity  ? 

13.  It  has  been  estimated  that  a  typhoid  fever  germ 
may  travel  about  2,000  times  its  own  length  in  one  hour. 
A  cholera  germ  may  attain  a  speed  that  is  45  times  as 
great  as  that  of  the  typhoid  bacillus.     If  a  man  should 
travel  as  many  times  his  own  length  as  the  typhoid 
bacillus  or  cholera  spirillum,  how  far  would  he  travel  in 
one  hour  ?* 

*From    Bevgen    and    Caldwell,    Practical    Botany,    Ginn    and 
Company. 


CHAPTER  L 

SANITATION 

Importance.  Sanitation  is  a  study  of  the  conditions 
which  make  for  the  health  of  a  community.  The 
greatest  prosperity  can  not  come  to  any  community 
until  every  precaution  is  taken  to  promote  and  to 
establish  public  health.  It  is  much  more  important 
that  we  should  prevent  diseases  than  it  is  that  we 
should  cure  them.  Many  times  as  much  money  is  now 
spent  in  attempting  to  cure  diseases  than  there  is  in 
preventing  their  spread.  It  is  only  recently  that  the 
public  has  begun  to  realize  the  advantages  in  pre- 
vention and  methods  of  control.  There  is  still  an 
annual  loss  from  infectious  diseases  of  millions  of 
dollars,  and  the  death  of  hundreds  of  thousands  of 
persons  in  our  communities,  .conditions  which  produce 
untold  suffering  and  sorrow. 

Preventable  diseases.  All  infectious  or  contagious 
diseases  are  preventable  diseases.  By  that  we  mean 
that  their  spread  can  be  prevented.  The  preventive 
methods  used  depend  upon  the  way  in  which  the  germs 
can  be  destroyed  and  the  way  in  which  they  are  carried. 

Destruction  of  germs.  There  are  many  methods  of 
destroying  germs  and  still  more  methods  of  preventing 

421 


422  A  YEAR  IN  SCIENCE 

their  rapid  growth  if  they  are  not  destroyed.  The 
simplest  and  one  of  the  most  effective  measures  for 
killing  germs  is  heat.  Fortunately  germs  can  not 
withstand  a  boiling  temperature,  and  if  dry  heat  or 
boiling  water  is  applied  for  about  an  hour,  they  will 
be  destroyed.  Ordinary  cold  temperatures  do  not  kill 
germs,  but  they  do  prevent  their  rapid  multiplication. 
Drying  is  destructive  to  many.  Light,  especially  bright 
sunshine,  kills  most  microbes  in  a  few  hours.  Many 
poisons  known  as  antiseptics  and  disinfectants  are  also 
used. 

Disinfection.  The  process  of  destroying  germs  is 
called  disinfection.  People  do  not  generally  realize  the 
necessity  of  careful  disinfection  during  and  after 
disease.  Because  disinfection  is  so  frequently  neglected 
preventable  diseases  continue  to  attack  mankind.  A 
little  more  care  in  this  direction  would  save  many 
lives. 

The  simplest  methods  for  disinfection  are  boiling  and 
airing  clothing  and  bedding  in  the  bright  sunlight. 
Most  methods,  however,  depend  upon  the  use  of 
poisons.  The  method  used  generally  depends  upon  the 
nature  of  the  particular  disease.  For  example,  in 
tuberculosis,  pneumonia,  or  colds,  the  sputum  should  be 
burned.  Handkerchiefs  or  any  clothing  containing 
discharges  from  the  nose  or  throat  should  be  thor- 
oughly soaked  in  an  antiseptic  or  boiled,  and  should 
not  be  put  in  with  the  common  laundry  before  this  is 
done.  In  diseases,  such  as  typhoid  fever  or  cholera, 


SANITATION  423 

all  discharges  from  the  intestines  should  be  disin- 
fected. Dishes  used  by  persons  having  an  infectious 
disease  should  always  be  scalded. 

Many  different  poisons  are  used  for  killing  germs 
though  they  are  not  all  suited  for  the  same  disease. 
One  of  the  most  frequently  used  of  these  disinfectants 
is  mercury  bichloride  (corrosive  sublimate).  Car- 
bolic acid,  lysol,  alcohol,  formalin,  boracic  acid,  and 
chloride  of  lime  all  serve  this  purpose.  If  it  becomes 
necessary  to  disinfect  a  house,  or  even  a  room,  a  gaseous 
disinfectant  must  be  used.  This  process  of  destroying 
germs  by  fumes  or  poisonous  vapors  is  fumigation. 

Fumigation.  The  two  most  common  agents  used  in 
this  process  are  formalin  and  burning  sulphur.  The 
room  should  be  tightly  closed,  bedding  and  clothing 
should  be  spread  out.  Formalin  can  then  be  intro- 
duced into  the  room  as  a  vapor;  as  an  easier  method 
of  getting  the  gas  into  the  room,  formalin  may  be  spread 
on  a  sheet  and  allowed  to  evaporate. 

Sulphur  dioxide  is  made  by  the  burning  of  sulphur 
' '  candles. ' '  A  better  and  safer  way  is  to  obtain  liquid 
sulphur  dioxide.  If  this  is  poured  out  into  dishes,  it 
will  soon  evaporate  and  fill  the  room  with  the  sulphur 
dioxide  fumes.  For  thorough  fumigation  a  room  should 
be  kept  closed  for  several  hours.  This  will  destroy 
all  vermin  as  well  as  germs. 

Quarantine.  We  prevent  the  spread  of  the  most 
infectious  diseases  by  keeping  people  suffering  from 
such  diseases  away  from  other  people;  that  is,  we 


424  A  YEAR  IN  SCIENCE 

isolate  or  quarantine  them.  If  a  house  is  quarantined, 
persons  can  not  go  into  or  out  of  it  for  fear  that  they 
may  carry  the  germs  to  others.  We  now  maintain 
strict  quarantine  for  such  diseases  as  smallpox,  diph- 
theria, and  scarlet  fever. 

Quarantine  frequently  causes  great  personal  incon- 
venience, but  we  should  all  be  public  spirited  enough 
to  be  willing- to  make  whatsoever  sacrifices  are  neces- 
sary to  keep  from  spreading  diseases  to  those  around 
us. 

Food.  It  is  impossible  for  us  to  supervise  personally 
the  production  or  even  the  preparation  of  all  of  our 
food.  The  food  which  we  eat  has  in  most  cases  passed 
through  the  hands  of  many  individuals,  and  in  some 
instances  through  many  processes  before  it  is  taken 
into  our  bodies.  The  possibility  of  germs  entering  the 
food  is  thus  very  great.  In  our  homes  we  can  protect 
ourselves  from  infection  by  being  careful  in  its  prep- 
aration. Cooking  sterilizes  food.  If  eaten  raw,  foods 
should  be  carefully  washed.  In  purchasing  our  table 
supplies,  it  is  advisable  to  patronize  only  those 
markets,  bakeries,  and  fruit  stores  which  are  kept 
clean.  Our  only  .means  of  protection  from  infection  in 
restaurants  or  hotels  is  to  select  those  which  are  clean 
and  sanitary. 

Insects  and  disease.  We  now  know  that  many 
diseases  are  carried  by  insects,  the  most  common  of 
which  is  the  common  house  fly.  To  this  little  insect 
with  its  filthy  habits  may  be  traced  the  spread  of 


SANITATION 


425 


many  diseases,  especially  typhoid  fever.  The  mosquito 
carries  malaria  and  yellow  fever  germs.  Sleeping 
sickness,  common  in  the  low  lands  of  Africa,  is  spread 
by  the  tse-tse  fly.  The 
flea  is  responsible  for  car- 
rying bubonic  plague. 

The  fly  lays  her  eggs  in 
all  sorts  of  decaying  mat- 
ter, manure,  garbage, 
dead  animals,  etc.  In  a 
very  short  time  these 
hatch  and  develop  into 
mature  insects.  The  body 
covered  with  hairs  and 
spines,  and  most  of  its 
habits,  particularly  adapt 
the  fly  for  collecting  and 
distributing  germs.  It 
feeds  in  all  manner  of 
dirty  places,  and  in  so 
doing,  eats  many  germs 
and  gets  its  feet  covered 
with  many  more.  These 
it  may  deposit  upon  our 
food  either  by  shaking 
them  off  its  feet  as  it 
walks  over  the  food  or 
dishes,  or  in  its  " specks"  which  always  contain  many 
germs.  If  by  chance  the  fly  has  visited  a  sick  room 


Adult. 
Permission    of     U.    S.    Dept.    of 

Agriculture. 

Fig.   188.      Life  history  of  house 
fly. 


426 


A  YEAR  IX  SCIENCE 


before  it  reaches  our  kitchen,  we  may  be  certain  it  is 
bringing  with  it  hundreds  of  disease  producing  germs. 
Until  we  get  rid  of  flies,  it  is  very  important  that  by 
screening  we  keep  them  away  from  our  food  and  away 
from  the  sick  room. 


Fig.  189.  Foot 
of  a  fly,  showing 
hooks,  hairs,  and 
pads  to  which 
germs  easily  ad- 
here. 


Permission   U.  S.   Dept.    of  Agriculture. 

Fig.    190.      Gelatine    plate    showing    bac- 
teria  in   fly   foot   prints. 


The  most  effective  way  of  abolishing  this  pest  is  to 
prevent  it  from  breeding.  This  can  be  done  by  remov- 
ing the  dirty  places  in  which  it  breeds.  Manure  and 
garbage  should  be  kept  in  closed  cans  or  boxes,  and 
frequently  removed  and  destroyed.  The  neighborhood 
should  be  kept  clean  and  sanitary  so  that  the  fly  can 
not  find  a  place  in  which  to  lay  her  eggs.  Any  cam- 
paign against  the  fly  must  be  directed  against  filth  as 
well  as  against  the  adult  fly. 


SANITATION 


427 


The  mosquito  is  responsible  to  a  large  extent  for  the 
spread  of  two  diseases,  malaria  and  yellow  fever. 
When  it  pierces  the  skin  of  a  sick  person,  germs  are 
taken  into  its  body.  These  may  then  later  be  injected 
into  the  body  of  a  well  person. 

The  eggs  of  the  mosquito  are  laid  on  the  water. 
These  soon  hatch  into  "  wrigglers. "  which  later  develop 


Fi&r  191.  Life  history  of 
common  mosquito.  A,  B,  eggs ; 
C,  E,  larvae;  D,  pupa;  F, 
adult.  After  Howard. 


Fig.  192.  A,  position  of 
malaria  mosquito  (Ano- 
pheles) -when  at  rest,  B, 
position  of  common  house 
mosquito  (Culex)  when  at 
rest.  After  Howard. 


into  the  adult  mosquito..  The  wriggler  lives  in  the 
water,  but  it  must  frequently  come  to  the  surface  to 
get  air.  To  get  rid  of  the  mosquito  we  must  destroy 


428  A  YEAR  IN  SCIENCE 

its  breeding  places.  Swamps  and  ditches  must  be 
drained;  rain  barrels,  open  wells  or  any  receptacles 
holding  water  should  be  carefully  screened.  The 
wrigglers  can  be  destroyed  by  a  film  of  oil  on  the  water. 
This  enters  the  breathing  pores  and  readily  kills  the 
larvae. 

Yellow  fever  has  practically  been  stamped  out  of 
New  Orleans  by  these  measures.  Some  of  the  earlier 
attempts  to  dig  the  Panama  Canal  were  futile  because 
of  the  prevalence  of  yellow  fever.  When  operations 
were  finally  begun  by  our  government,  one  of  the  first 
things  which  it  did  was  to  rid  the  region  of  the  yellow 
fever  mosquito. 

Milk.  Milk  is  very  easily  contaminated  with  germs. 
Many  children's  diseases,  typhoid  fever,  and  tuber- 
culosis, are  spread  by  infected  milk.  Consequently 
the  death  rate  for  babies  and  young  children  is  very 
great.  Every  care  possible  should  be  taken  to  see 
that  the  milk  which  they  use  is  free  from  germs.  In 
summer  the  milk  must  be  kept  cool  to  prevent  its 
"spoiling,"  and  the  bottles  used  for  feeding  the  babies 
must  also  be  sterilized. 

Water.  The  source  of  drinking  water  in  large  cities 
is  very  frequently  from  rivers  or  lakes.  This  makes  it 
very  liable  to  contamination  from  sewage,  and  sewage 
is  almost  certain  to  contain  germs  of  typhoid  and  other 
diseases.  City  water  should  be  frequently  examined  to 
see  that  it  contains  no  germs.  If  it  is  known  to  be  bad, 
or  even  suspected,  it  is  wise  to  boil  the  water  before 


SANITATION  v    429 

using  it.  In  smaller  communities  and  in  the  country 
where  wells  are  used,  it  is  necessary  to  guard  against 
contamination  of  the  water  from  the  barn  yard,  privy, 
or  cess  pool. 

The  Board  of  Health.  Since  cities  were  first  organ- 
ized people  have  recognized  the  need  of  some  kind 
of  protection.  Accordingly,  laws  have  been  made  for 
governing  the  people,  for  protecting  property,  and  in 
fact  for  protecting  individuals  from  attack  and  murder. 

Only  recently,  however,  have  we  come  to  recognize 
the  necessity  of  having  laws  and  regulations  for  pro- 
tecting the  public  health.  It  is  almost  as  important 
to  prevent  your  neighbor  from  giving  you  the  small- 
pox as  it  is  to  prevent  him  from  injuring  or  possibly 
killing  you  in  some  other  way.  Nearly  every  com- 
munity now  has  a  Board  of  Health,  the  duty  of  which 
is  to  protect  the  health  of  the  people.  Persons 
appointed  from  the  community  constitute  this  board. 
One  of  the  number,  the  health  officer,  is  required  to 
see  that  certain  laws  are  enforced  to  prevent  the  spread 
of  contagious  diseases.  It  is  his  duty  to  placard  houses 
in  wrhich  are  contagious  diseases.  Before  the  quaran- 
tine is  removed  he  must  disinfect  the  house. 

It  is  the  duty  of  the  health  board  to  inspect  all  milk ; 
to  prevent  the  sale  of  unhealthful  milk;  to  see  that  all 
garbage  and  sewage  are  properly  disposed  of;  and  to 
provide  a  pure  supply  of  water.  All  persons  should  obey 
the  instructions  of  the  Board  of  Health.  This  board 
needs  the  assistance  of  each  individual  in  the  community. 


430  A  YEAR  IX  SCIENCE 

The  carelessness  of  just  one  individual  may  be  the  cause 
of  much  sickness  and  many  deaths. 

Questions 

1.  Name  ten  preventable  diseases. 

2.  To  what  extent  is  a  community  responsible  for 
the  spread  of  such  diseases? 

3.  State  six  methods  of  destroying  germs. 

4.  What  is  a  disinfectant  ?  Name  five  disinfectants. 

5.  How  should  a  room  be  fumigated? 

6.  What  should  be   our  attitude  toward  quaran- 
tine?   Why? 

7.  How  can  we  guard  against  infection  from  foods  ? 

8.  Discuss  the  relation  between  insects  and  diseases. 

9.  How  may  milk  become  contaminated?     What 
diseases  may  be  spread  by  milk? 

10.  Are  there  any   objections   to   running   sewage 
into  bodies  of  water  from  which  the  water  supply  for 
the  city  is  obtained? 

11.  Are  there  better  methods  for  disposing  of  sewage  ? 

12.  When  should  one  use  only  boiled  w^ater? 

13.  Learn  what  you  can  of  the  work  done  by  the 
Board  of  Health  in  your  city. 


INDEX 


Abdomen,   317 

Absorption  of  food,  278,  325 
Accommodation  of  eye,  404 
Acids,  105 

characteristics  of.   106 
Adaptation  of  animals,  252 

of  plants.  222 
Adenoids.   354 
Adrenal  bodies.  368 
Adrenalin,  368 
Adult,  262.  267,  374 
Adulteration  of  food,  307 
Agassiz,  Alexander,  130 
Age  of  man,  295 
Air,  as  matter,  2 

comparison    of    inhaled    and 
exhaled,  351,  352 

composition  of,  121 

importance  to  plants  and  ani- 
mals. o4."> 

-ae.  340 

storage  by  plants,  216 
Alcohol  as  a  stimulant,  330 
Alimentary    canal,    of   animals. 
276 

of  man,  310 

Ameba.   272.   279.   280,   282 
Amphibians,  261 
Anatomy,  definition  of.  296 
Anchorage  of  plants.  222 
Animal     life     dependent     upon 

water,   115 
Animals,  adaptation  of,  252 

change  due  to  new  conditions, 
252 


classification  of,  254ff. 

distribution  of,  249ff. 

life  processes  in,  272ff. 

relation   to  man,   286ff. 

unable     to     maintain     their 

ground,   251 
Anther,  234 
Anticyclone,  142 
Antiseptics,  422 
Antitoxin,  414,  416 
Aorta,  340 
Appendix,    318 
Argon,  121 
Arm,  bones  of,  372,  373 

muscles   of,   379 
Arteries,  339,  340,  342,  368 
Arthropods,  264 
Astigmatism,  405 
Atmosphere,      composition      of, 
121 

effect  on  earth's  surface,   164 

importance  of,  120 

moisture  in.  124ff. 

pressure  of,  129ff. 

properties  and  uses  of,  121 

variations  in,  120 
Auditory  canal.  406 
Auricles.  338 

Bacteria.  243 

b.  and  disease,  245 
conditions  for  growth  of,  245 
decay  due  to,  246 
for  diphtheria,  416 
in  lymph  glands,  368 


431 


432 


INDEX 


in  waste  products,  325 

skin  as  a  protection  against, 
359 

useful  b.,  103,  247 
Bacteriology,  definition   of,  243 
Barometer,   134 
Bases,   106 
Bile,  319,  324 
Birds,  257 
Bladder,  358 
Blade,  200 
Blizzards,  142 
Blood,  334 

amount  of,  337 

coagulation  of,  337 

supply  in  muscles,   379 

vessels,  334,  342 
Board  of  Health,  429 
Boiling  points,  27,  40,  42 
Bones,  cells  of,  374 

composition  of,  72,  373 

diseases  of,  375 

division  of,  371 

fracture  of,  376 

growth  of,  374 

of  limbs,  372 

purpose  of,  370 
Botany,  1,  193ff. 
Brains,  of  aniirals,  281 

of  man,  384,  385,  386,  387 
Bread-making,  70 
Breathing,  mechanism  of,  349 
Breezes,  land  and  sea,  140 
Bronchus,  348 
.Burning,  94 
Butterfly,  development  of,  266 


Calorie,  definition,  31,  44 

of  heat  in  food,  305 
Calyx,  233 


Canal,  alimentary,   310 

of  ear,  406,  408 
Capillaries,  342 
Carbohydrates,  203,  204,  301 
Carbon,  kinds  of,  60ff. 
Carbon  dioxide,  66,  93,  204 

balance  maintained,  68 

commercial  uses  of,  68,  123 

in  air,  66,  68,  121,  123,  351 

in  blood,  357 

test  for,  67 
Carpal,  372,  373 
Cartilage,  373 
Cast  iron,  87,  88 
Cell,  egg  and  sperm,  283 

of  a  plant,   196 

of  animals,  275 

nerve,   384 
'    wall,  195 
Cerebellum,  386 
Cerebrum,  386 
Charcoal,  61 
Chemical,  affinity,  58 

analysis,  57 

changes,  52 

compounds,  53,  54 

properties,  53 

synthesis,  57 
Chemistry,  2,  51ff. 
Chlorophyll,  202,  203,  201,  301 
Choroid,    400 
Chrysalis,  266 
Circulatory    system,    334tf. 
Circulation  in  animals,  279 
(lay,  190 
Climate,   149,  150 
Clothing,     animals     supplying. 
288 

use  of,  365 
Clouds,  126 
Coagulation,  337 


INDEX 


433 


Coal,  formation  of,  62,  63,  64 
Cochlea,  408 
Coelenterates,  269 
Coke,  64,  65 
Complex  animals,  274 
Condensation,  46 
Conduction,  20,  22 
Continents,  160,  162 
Convection,  22,  138,  139 
Cooking,   307 
Corals,  198,  269 
Corolla,  233 

Corpuscles,    destroying    germs, 
414 

red,  335 

touch,  397 

white.  336,  368,  414 
Cortex,  227.  228 
Crayfish,  264 
Cretinism,  368 
Crops,  animals  injurious  to,  289 

rotation  of,  222 

value  in  U.  S.,  206 
Crustacea,   264 
Crystalline  lens,  400 
Cyclones,  141 

Darwin.  Charles.  236 

Day,  151 

Decay,  due  to  bacteria,  246,  308 

Dendrites,  384 

Dermis,  360 

Dew.  125 

point,  125 
Diabetes..  369 
Diamond,  65 
Diaphragm,  317 
Diffusion,  6,  9,  10,  11,  221.  322, 

323.  324,  325 
Digestion,  absorption,  325 

in  animals,  276 


in  intestine,  324 

in  mouth,   322 

in  plants,  207 

in  stomach,  323 

large  intestine,  324 

necessity  of,  312 
Digestive  system,   310ff. 
Disease,  cause  of,  411 

contagious,  354 

due  to  bacteria,  245 

due  to  insects,  424 

due  to  worms,  308 

germs,  412,  413,  414,  421 

health  and  d.,  41  Iff. 

immunity  from,  419 

medicines,  417 

of  bones,  375 

of  glands,  368,  369 

of  respiratory  organs,  353 

of  the  ear,  409 

of  the  eye,  405 

preventable,  421 

produced  and  carried  by  ani- 
mals, 289 

some  methods  of  prevention, 
422,  423,  424 

treatment  of,  415,  416 
Disinfection,   422 
Dislocation  of  bone,  377 
Distillation,  41 
Dust,  121,  124?  164 

Ear,  drum,  407 

structure,  406 
Earth,  orbit  of,  152,  153 

surface  of.    160ff. 
Echinoderms,  268 
Education.  394 
Eggs,  development  of,  283 

fertilized,  235,  262,  283 
Electrolysis,  110 


434 


INDEX 


Elements,  53,  55 

carbon  as,  60 

hydrogen  as,  97 

in  food,  298 

iron  as,  85 

nitrogen  as,  101 

number  of,  56 

oxygen  as,  90 

phosphorus  as,  72 

sulphur  as,  77 
Enzymes,  322,  323,  324 
Epidermis,  360 

of  leaf,  201 
Epiglottis,  348 
Esophagus,  310,  317 
Eustachian  tube,   317,  407 
Evaporation,  44,  124,  208,  209, 

213,  364 

Evans,  Dr.  W.  A.,  117 
Excretion  in  animals,  280 

in     man,  357ff. 

in  plants,  221,  222 
Excretory  system,  35711'. 
Exercise,  necessity  of,  381 
Eyes,  of  animals,  281 

of  man,  399 
care  of,  405 
defects  of,  405 
structure,  400 

Fatigue,  381 

Fats,  302,  323,  324,  326 

test  for,  302 

Fauna,  definition  of,  249 
Femur,  373 
Fertilization,  235 
Fibula,  373 
Fire  extinguisher,  69 
Tireless  cookers.  21 
Fishes,  263 
Flowers,  232 


Fly,  abolishment  of,  426 

development  of,  425 
Focus,   402,   403 
Fog  and  clouds,  126 
Food,  absorption  of  by  animals, 
278 

adulteration,  307 

composition   of,   304ff. 

cooking  of,  307 

diffusion  of,  322,  325 

digestion  of  by  animals,  276, 
277 

elements  in,  298 

manufactured  by  plants,  203, 
206 

protection  against  infection. 
424 

quantity  and  kind  of,  306 

selection  of,  306 

storage  of,  205 

stuffs,  299fT.-326 

supplying  animals.  287 

uses  of,  198,  207,  298,  305 
Frost,  125 
Fumigation,  423 
Fungi,  243 
Furnace,  blast,  86 

phosphorus,  73 

Ganglia,  384 

Gases,  boiling  points  of,-  40,  42 

change  from  liquid  to  g.,  35 

change  in  volume,  47 

effect  of  temperature  upon,  18 

molecules   in,    10 
Gastric  juice,  323 
Germicides,  414 
Germs,  412,  413,  414,  421 
Glands,  adrenal,  268 

definition  of,  277 

digestive,  310,  311 


INDEX 


435 


ductless,   367ff. 

gastric,  311,  318,  323 

intestinal,  311,  324 

liver,   311,  319 

lymph,  367 

pancreas,  369 

salivary,  316 

spleen,  369 

sweat,  361 

thyroid,  368 
Glottis,  347 
Glycogen,  326 
Goiter,  368 
Graphite,  65 


Habitat,  211 
Habits,  391 
Hail,  126 
Hair,  361 
Head,  371 

Health,  117,  316,  325,  331,  355, 
365,  381,  405,  409,  41  Iff., 
42  Iff. 

Board  of,  429 
Heart,  334ff. 
action  of,  340 
beat,  340 
structure,  338 
Heat,  effect  of,  on   liquids,   15, 

44 

effect  of,  on  solids.   13 
given  off  in  condensation.  40 
necessary  to  change     ice      to 

water,  37 
necessary  to  change  water  to 

steam,  44 

necessary  to  dissolve  a   sub- 
stance, 38 

source    of   in   the   body.    363, 
380 


transfer  of,  conduction.  20,  22 
convection,  22 
through  air,  124 
unit  of  h.  measure,  31 
withdrawn  in  evaporation  of 

liquids,   44 

Heating,  effect  of  unequal,  139 
Hemoglobin,  336,  351 
Hemorrhages,    368 
Host,  243 
Humerus,  372,  373 
Humidity,  124 
Humor,   aqueous   and   vitreous, 

401 

Hydrochloric  acid,  98 
Hydrogen,  97ff. 
Hygiene,  definition  of,  296 
of  the  skeleton,  375 

Ice,  38,  39,  45,  47 
Images,  402,  403 
Insects,   264,  265,   424ff. 
Intestine,  310,  311,  318,  324 
Invertebrates,  255 
Involuntary  action,  389,  390 
Iris,    400 
Iron,  84ff. 

oxide  of,   94,   168 

sulphide,   54,  55 
Irrigation,    144 
Isobar,  155,  156 
Isotherm,    156,    158 

James,  Professor,   392 
Jenner,  355,  417 
Joints,  227,  375 

Kahlenberg,    121 
Kidneys,  357 

Lampblack,  62 
Larva,  266,  428 


436 


INDEX 


Larynx.  348 

Leaves,  bloom  of,  214 

chlorophyll,    202,    203,    204, 
301 

excretion,  280 

food-making  power,  203 

food  storage,  205 

motion,  280 

protection     against     loss     of 
water,  213 

relation  to  water  supply,  211 

respiration,  215 

structure  of,  200 

transpiration,  208 
Lens,  402 
Ligaments,  375 

sprain  of,  377 
Light,  401,  402 
Lightning,  143 
Lime  water,  53,  68 
Limbs,  bones  of,  372 
Liquids,   boiling  points   of,   40, 
42 

change  from  solids,  35 

change  in  volume,  47 

change  to  gas,  35 

effect  of  heat  on,  15,  16,  44 

entering  plants,  230 

heat    given    off    when    1.    be- 
come solids,  38 

heat  withdrawn    in    evapora- 
tion of,  44 

melting  points  of,  39 

molecules    in,   9 
Litmus,  106,  107 
Liver,  311,  319,  326 
Loess  beds,  164 
Lungs,  347,  348,  349 
Lymph,  334,   335 

glands,  367 

vessels,  334,  342,  343 


Mammals,  255 

Man,  age  and  races  of,  295 
body  of,  296 
classification  of,  294 
difference     between     in.     and 

other  primates,  294 
relation  of  animals  to,  286 

Manganese  dioxide,  92 

Matches,  74,  75,  76 

Matter,  classification  of,  53 
constitution  of,  6 
definition  of,  2  • 
effect   of   heat   on,    13 
molecular  theory  of,  7 
physical   and  chemical 

changes,    51 
three  forms  of,  3,  34 

Mechanical  mixtures,  53 

Medicines,  417 
patent,  418 

Medulla  oblongata,  386 

Melting  points,  27,  39,  81 

Mercury,  boiling  point,  40 
melting  point,  40 
use  in  barometer,  134 
use   in    thermometer,    27 

Mercuric  oxide,  92 

Mesentery,  319 

Metacarpals,   372,    373 

Metatarsals,  373 

Milk,  action  of  rennin  on,   32:* 
composition  of,  300 
contamination  of,  428 
pasteurization  of,  308 

Molecular  theory,  7 

Molecules,  8,  9,  10,  11,  24,  48 

Mollusks,  267 

Mortality     list     for      Chicago 
1910,    355 

Mosquito,   development   of.   42, 
protection  against,  428 


INDEX 


437 


relation  to  disease,  427 
Motion  of  animals,  280 
Mountains,   162 
Mouth,  digestion  in,  322 

of  animals,  276 

of  man,  310,  312 
Mucous    membrane,    312,    316, 

318,   348 

Mucus,  312;  316,  322 
Muscles,  ciliary,  404 

in  walls  of  arteries,  368 

protection  of,  359 
Muscular  system,  378ff. 

Xails,  363 
Narcotics,  328ff. 
Natural  science,   1 
Nerves,  auditory,  408 

cranial,   387 

motor,  385 

of  animals,  281 

olfactory,    399 

sensoiy,  385 

supply    of    in    muscles,    379 
Nervous    system,    383ff. 
Nervousness    due    to   eyes,    405 
Neurons,  384 
Neutral  substances,  107 
Neutralization,   107 
Nicotine,  328 
Night,   151 
Nitric  acid,   106,  108 
Nitrogen,  in  air,  101,  102,  103, 

121,  122 

Nose  cavity,  348 
Nostrils,  347 
Nucleus,  196 
Nutrition,  207 

Oceans,   160 
Oils,  302,  323 
test    for,    302 


Olfactory  nerves,  399 
Opium,  329 

Orbit  of  earth,  152,  153 
Organs,  coordination  of,  383 

definition  of,  275 

in  body  cavity,  311 
Oxidation,  345~  380 

definition  of,  93,  94 
Oxides,  58,  66,  82,  85,  92,  93, 

94,  102,  106,  168 
Oxygen,  90ff. 

attack  on  rocks,  168 

given  off  by  plants,  204 

in  air,  68,  90,  95,   121,   122, 
351 

uses  of,  94,  121,  122 
Ovary,  234 
Ovule.  234 
Oysters,  267 


Palate,   hard   and  soft,   312 
Pancreas,  311,  319,  369 

juice  from.  324 
Papillae,  397.  398 
Parasites,    243 
Paramoecium,  274 
Pasteurization,  308 
Peat,  64 
Pepsin,   323 
Periosteum,  374 
Peritoneum,  319 
Perspiration,  360 
Petal,  233,  234 
Petiole,  200 
Phalanges,  373 
Pharynx,   317 
Phosphorus,  72ff. 
Physical  changes,  51 

geography,  2,   120ff. 

properties,  53 


438 


INDEX 


Science,  1 

Physiology,  definition  of,  296 
Pistil,    234 
Pith,   227,   228 
Plains,  163 
Plant      life      dependent      upon 

water,  115,  198,  211 
Plants,  air  storage  of,  216 

comparison  with  animals,  197 

composition  of,  195ff. 

food,  198,  206 

importance  of,  193,  205  242ff. 

leaves,   200ff. 

reproduction  of,  232ff. 

respiration  of,  215 

roots,   219ff. 

stems,  225ff. 

transpiration  of,  208 

protection    against   loss   of 
water,    213 

waste  products  of,  216,  221 
Plasma,   334,  335 
Plateaus,   163 
Pleura,  349 
Pleurisy,  354 
Pollen,  234 
Pollination,  236 
Pons  varolli,  386,  387 
Porifera,  269 
Potassium    chlorate,    92 
Potassium  hydroxide,  106 
Pressure,  atmospheric,   129 

column   of   mercury   held   by, 
133 

effect    of    change    on    boiling 
point,  42 

regions  of  high  and  low,  142 

variations   in   p.   due  to  ele- 
vation,  134 
Priestley,  Joseph,   92 
Primates,  294 


Proteins,  206,   299,   323,   324 

test  for,  300 

Protoplasm,  195,  196,  197,  272, 
305 

composition   of,    196 
Protozoa,  270,  412 
Ptomaines,   308 
Pulse,  342 
Pupa,  266 

Quarantine,    423 

Radius,  372,  373 
Rain,   126 

amount  of  in  U.  S.,   146 

distribution  of,  172 

effect  of  winds  on,  144 

work  of  r.  in  causing  relief, 

169 

Rainbow,   143 
Reflex  action,  390 
Refraction,  402 
Rennin,  323 
Reproduction,  definition  of,  282 

of   animals,    281 

of  plants,  232,  234,  235,  236, 

238 

Reptiles,    260 

Respiration,  external  and  inter- 
nal, 346 

of  animals,  278 

of   plants,    216 

organs   of,    347 
Respiratory  system,  345ff. 
Ribs,  372 
Rickets,    376 
Rind,  228 
Rocks,  186,  189 

chemical  effect  on,  168 

effect  of  change  of  tempera- 
ture on,  167 


INDEX 


439 


Roots,  absorption  through,  220 

anchorage,  222 

definition  of,  219 

excretion  through.  221 

structure  of,  220 
Rust,  94,  168 

Saliva,  316,  322,  323 
Salts,  107,  302,  357 
Sand,  165,  190 

dunes,  165 
Sanitation,  42 Iff. 
Saprophyte,  243 
Saturation  of  atmosphere.  125 
Science,  definition  of,  1 
Seasons,  152 
Secretions,   in   the   mouth,   316 

internal,  367,  368 
Seed  dispersal,  238 
Seeds,  formation  of,  234 
Senses,  the  special,  397ff. 
Sensitiveness,  of  animals,  281 

of   man,   399 
Sepal,  233 
Serums,  415 
Skeletal   system,   370ff. 
Skin,  care  of,  365 

structure  of,   360 

uses   of,    359 
Smell,  399 
Snow,   126 

Sodium  hydroxide,  106,  108 
Soil,  kinds  of,  190,  191,  192 

Dryer's  classification  of,  192 

origin  of,  186 
Solar  plexus,  389 
Solids,   change   in   volume,   47 

change  to  liquids,  35,  37 

effect  of  heat  on,  13 

heat   given   off  when   liquids 
become  s.,  38 


heat  necessary  to  dissolve,  38 

melting  points,  39 

molecules  in,  8 
Solutes,  187,  188,  206,  219.  220, 

302,  322 

Spiders,  264,  267 
Spinal  cord,  384,  387 
Spleen,  369 
Sponges,  198,  269 
Sprain,  377 
Stamen,  234 
Starch,  digestion  of,  324 

formation   of  in  plants,  204, 
301 

test  for,  301 
Steel,  87,  88 
Stems,  functions  of,  225 

kinds  of,  225 

structure  of,  227 
Sun  as  a  source  of  heat,   124, 

150 

Sterilize,  245,  247,  308,  428 
Sternum,  372 
Stimulants,    328ff. 
Stomach,  310,  317,  323 
Stomate,  201,  202,  214,  215 
Storms,  137ff. 

definition,   141 

kinds  of,   142 

Streams,  effect  on  human  ac- 
tivities,   182 

development,    175,    178,    179, 
181 

erosion,  172 
Sugar,  301,  324,  326,  369 

test  for,  301 
Sulphur,  77ff. 

dioxide,  94 

Talus,   168 
Tarsals,  373 


440 


INDEX. 


Taste,   398 
Teeth,  312,  314 

care   of,   315 

structure    of,    3i4 
Temperature,  boiling  points,  40, 
42 

condensation,  46 

effect  of  on  gases,  18 

effect  of  on  rocks,  167 

effect  of  heat  on  liquids,   15, 
16,  44 

effect  of  heat  on  solids,   13 

effect  of  t.  on  climate,  150 

measurement  of,   26 

melting   points,    39 

regulation   of   360,   363,    364, 

398 

Tendon,  378,  379 
Thermometer,  Air,  26 

centigrade,  27,  28,  29,  30 

Fahrenheit,  27,  29,  30 

determination  of  fixed  points, 
28 

Galileo's,  26 

range  of  mercury  t.,  31 
Thermos  bottle,  21,  24 
Thorax,  317 
Throat  cavity,  310,  317 
Thunder,    143 
Thunderstorms,  142 
Tibia,  373 

Tissues,  definition  of,  196,  275 
Tobacco,   328 
Tongue,  316,  398 
Tonsils,  317,  354 
Tornadoes,    142,    144 
Touch,  397 
Trachea,  347,  348 
Trade  winds,   140 
Transpiration,    208,    209 
Trichina,  308 


Trunk,  371 
Tuberculosis  354,  376 
Typhoid  and  flies,  425,  428 

Urea,  357 
Ureter,  358 
Urethra,    358 
Urine,   358 
Uvula,  312 

Vaccination,  355,  417 
Vaccines,    416 
Valves  in  heart,  340 
Vascular  bundle,  228,   229 
Veins,  200,  339,   340 
Ventilation,  352 
Ventricles,   338 
Vertebrae,    371 
Vertebrates,  254 
Vessels,  blood,  324,  342,  368 

lymph,  324,  342,  343 
Villi,  326 
Vocal  cords,  348 
Volume,  changes  in,  47 
Voluntary  action,  390 

Water,    11  Off. 

absorbed  by  roots,   220 
composition   of,    110 
contamination  of,  428 
dangers   in,    116 
factor  in  soil  formation,  187 
factor    in    starch     formation, 

204 

falls,  177,  179,  181,  183 
filtering   of,    117 
hard,   114 

in  the  human  body,  302,  257 
plant  and  animal  life  depend- 
ent upon,   115,   198,   211 
properties   and    uses   of,    111 


INDEX. 


441 


protection  against  loss  of  w. 

by   plants,       213 
quantity  of  on  earth,  110,  221 
soft,    114 
spouts,   144 
vapor    in    air,    121 


forecast,   154 

maps,    154,    156,    157 

explanation   of   maps,    155, 
158 

Weathering,  164,  187,  190 
Winds,    137ff. 


Waste  products,  of  plants,  216,      Worms,  268 


221 


in  food,  308 


in    the    body,    325,    340,    351, 

357,  359,  380  Yeast,  70 

Weather  Bureau,   154,   155 

definition    of,    149  Zoology,    1,   249ff. 


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